1. In this, the second edition of the Journal, we feature the Atmosphere. Every infrared spectroscopist worth his or her salt is well aware of the problems posed by atmospheric absorption, its intensity, and variations therein. Less dedicated practitioners run backgrounds and see water vapour and CO2 absorptions but quite probably ignore them.It turns out this can be hazardous, so we introduce this complex and difficult subject below. In the next Edition, after Christmas, we will take the matter further. Over the last few months an esoteric correspondence has appeared in Spectrochimica Acta about the role of CO2 in global warming. The letters have been almost incomprehensible to those who have no background in the subject, so I asked Jack Barrett to write us a piece describing his view of the importance that man-made CO2 has in influencing global warming. As you will see, Jack is rocking the boat pretty violently and his views will certainly not be acceptable to the Green Lobby. As a convinced thoroughbred Brownie, I must say I am delighted with the article. I can turn up the heating, buy a bigger car and leave the lights on without any qualms of conscience. My contribution to what is inevitable anyway is trivial. I suspect one or two readers might disagree - please write us a letter. In the first edition I contributed an article on sampling in FT-Raman spectroscopy and promised a follow up for Edition II. This time I have contributed my thoughts on heated and cooled cells. When a new journal starts up it is always hard to find good, really interesting, contributed articles. In Edition I we were lucky and here in Edition II we are fortunate also. The group at the University of Xiamen in China are famous for their work on Surface Enhanced Raman Spectroscopy (SERS), a valuable technique in biochemistry and some specialist areas of low level analysis. The problem with the method is that it works well if the surfaces used are copper, silver, or gold but has always proved to be very difficult over anything else. Electrochemists find SERS very interesting but find the restriction to copper, silver, or gold frustrating. Professor Tian and his colleagues are lifting this restriction, so their efforts have enormous potential. Even if you are not particularly involved in Raman spectroscopy, I recommend you have a look at this article. It could well turn out to be of major importance in the future. A journal appearing on the Internet has advantages and disadvantages
compared with its hard copy competitors. Once organised slickly (and we're working on it)
we can be faster and hence much more interactive. A correspondence column or a bulletin
board can be really topical. On the other hand, there can be problems with access due to
overloaded telephone lines and diagrams can be of poor quality. The problems will
gradually be solved but the advantages are real and they are expanding. Since Edition I appeared we have received several responses and these have already generated requests for information, so our Bulletin Board is under way! Now we need some letters, preferably contentious and challenging! A few weeks ago I visited Brisbane - my first visit to Australia - wonderful place - enjoyed every minute - especially a swim in the Pacific at 8 in the morning from an almost isolated, absolutely clean, vast, beach. My visit included the 2nd Australian Spectroscopy Meeting at Q.U.T. The lectures and posters were all on Vibrational Spectroscopy and of a quality and quantity that would be hard, if not impossible, to match in Europe or America. I deliberately "got at" the youngsters - told them to ignore their superiors - many of whom, like me, are probably computer illiterate - and to submit papers, which I am sure many will. To conclude - have a wonderful Christmas and a fabulous New Year. PATRICK AND WENDY. 2. The Big Spiders Guide to Vibrational Spectroscopy on the Web Gary Ellis Instituto de Ciencia y Tecnología de Polímeros, C.S.I.C., Madrid, SPAIN. E-Mail:gary@fresno.csic.es I remember that I was but a wee nipper when my Great Uncle Jim, whilst watching the waves crashing down on a lonely beach on the north-east coast of England, told me the secrets of the surf and how to count the galloping white horses. At around the same time, hoardes of bermuda-beshorted individuals humming catchy tunes obliged us to join their revolution, and my concept of surf changed. Now the internet generation has given us a more accessible definition of surfing - this time it's something that even Pat Hendra can do in his sitting room without getting his socks wet or sand in his ears! All one needs is a suitably connected PC, a rudimentary knowledge of Windows, a mouse, and an empty diary for the next few weeks. "Cybersurfing", "websurfing", "netsurfing"... or whichever buzzword you use, is eye-opening and informative fun, but it must undoubtably be filed into the "dangerous terminal activities" folder for its propensity to contradict our notions of time and space. It's staple diet is your precious time! Daily newspapers, "Hello", your favorite football team, tourism, Spinal Tap, the CIA, train-spotting, Oasis, Bovine Spongiform Encephalopathy, garlic lovers, The Goon Show, Bugs Bunny, MTV, they're all in there... even Margaret Thatcher and Antonio Banderas have "Home Pages" (not linked as far as I know). Maybe this isn't quite what you're looking for! Finding a "site" which satisfies your requirements is worth celebrating. It takes basic cybersurfing abilities, some dedication, and trips down more than several blind alleys before one can come up with anything justifiably useful. This said, it must be recognized that the WWW can and does provide some very interesting sources of reference, links to research centres with similar interests, commercial information, educational resources, etc., albeit mixed in with an enormous amount of completely irrelevant cyberjunk.
What about vibrational spectroscopy?.......Well, it's on the web too, and growing fast! Vibrational Spectroscopy, Web Style. The next few pages include a shortlist of web sites from my bookmarks which may be of interest, discovered whilst "surfing the web". The information is by no means complete, and is intended as a preliminary survey. If I missed yours... sorry! Access to all sites listed here is, as it should be, free of charge. Disclaimer: No responsibility can be taken by IJVS for the links, which may vary, and whose content is totally independant of both IJVS and the Publisher. By the way, if anyone knows of any interesting vibrational spectroscopy links not included here, send me an e-mail Academic Sites. A number of research groups working in vibrational spectroscopy have generated "home pages", whose intention is, on the whole, peer-informing.... just letting us know that they're out there! Such sites tend to provide general information about research activities, their instrumentation, and links to other sites which bear some relation. Most sites are still in the developmental stage, and some promise to be interesting. I am eager to see the Virtual Raman Spectrometer which is listed as a feature in the contents of the WWW Raman Server at the Universiy of Graz, Austria, still "under construction" after many months. Other examples of academic sites are:
The University of Newcastle includes a Spectroscopy Group Mailing List and discussion forum within the Mailbase project. Typical messages appearing on the bulletin board range from practical spectroscopic problems and conference/seminar announcements to job offers and recent PhD's looking for jobs. Although not limited to vibrational spectroscopy, it may be a useful contact point. Educational and Bibliographic Resources. A growing buzz-word on the web is "hypermedia". Educational hypermedia is becoming a reality, and already vibrational spectroscopy is appearing on the virtual teachers blackboard. An Analytical Spectroscopy Webcourse can be found under the Science Hypermedia Project, originally based at the Virginia Polytechnic Institute, USA The Wilson group at the University of California, San Diego, USA include a highly visual spectroscopy tutorial in the Physical Chemistry section of their comprehensive chemistry education resource. Some tips on the interpretation of IR spectra are provided by the California State University at Stanislaw, USA. A number of interactive tutorial exercises in spectroscopy, can be found at the Department of Chemistry of the University of the West Indies, Jamaica.
As far as reference spectra are concerned, the Arnold Engineering Development Centre in Tenessee, USA holds a comprehensive collection of IR spectra of hazardous air pollutants in the GRAMS (*.spc) file format, and David Sullivan from the University of Texas at Austin offers some IR spectra from his research in a variety of formats, including JCAMP-DX. Societies, Journals and Conferences. The Society of Applied Spectroscopy has a well-developed and informative site based at the Arizona State University, USA. It includes comprehensive information on the society, contents and abstracts from the society's journal, Applied Spectroscopy, a spectroscopic events calendar, a monthly newsletter, and subscription details, etc.The Coblentz Society can also be found. The Royal Society of Chemistry has a very well-established and comprehensive WWW site, and provides the contents, abstracts and feature articles from many of the societies publications, such as "Chemistry in Britain" and "Analysis Europa". Elsevier Science have a page for downloading program and data files submitted to Spectrochimica Acta Electronica, integrated in Spectrochimica Acta Part B. The company also provides a very useful free e-mail alerting service, providing contents listings, Spectrochimica Acta Part-A included. The only on-line vibrational spectroscopy journal is, of course, the Int. J. Vib. Spectrosc. Currently, the following information on vibrational spectroscopy-related conferences can be found on the web:
Commercial Sites. The instrument and accessory manufacturers have started to appear on the web, providing product information, commercial contact points, corporate information, a page for requesting technical information or application notes, and some links to other useful sites. To date, I have found the following companies on-line:
These sites seem to be in constant development, as might be expected. Nicolet, Bruker and PE probably have the most advanced services at this stage, with many photos of equipment, etc. The interactive applications note request pages really do work. I tried Nicolet, and a smiling representative appeared after about two weeks with a briefcase-full of literature!
Some laser and optical components specialists can also be located on the web: The Interlab site provides source data on analytical spectrometry and has a number of links to vibrational spectroscopy sites, including journals and software. Want to buy or sell second-hand spectroscopic equipment? The Internet Market Place for Physicists may provide an interesting market stall. Searching for Information. There are a variety of methods for searching for information on the WWW, generally known as "Search Engines". These are free to use, and normally simply require you to introduce a word or phrase, and hit the search button. One of the most useful is search.com, which includes many alternative solutions for Web-searching. Netscape's own Net Search also includes a large variety of alternative search routes. To find information about a specific topic, the web tip is "be specific". If you are looking for an IR spectral database and you just use a global word, like "spectra" you shouldn't be surprised if a search engine comes up with more than 70,000 documents for you to browse! Normally you are presented with a fairly irrelevant haystack of spurious information or cyberjunk. However, most search engines provide advanced search options, which allow you to place restrictions on date, site locations, and to search for strings and phrases, or threaded searches, so that you can dig out that obstinate needle. I think you may be surprised when you find out just how many vibrational spectroscopists there are on-line! Good luck and.... Happy Spectrosc-urfing! 3. Backgrounds Editor All infrared users should be familiar with their instruments' background. F.T.I.R.s are, in the traditional parlance, single beam instruments; the spectrum of the source unattenuated by a sample is scanned and then compared later with that of the source plus sample. The point by point ratio of the two spectra being the absorption spectrum of the sample alone. The software we all use frequently memorises the background and then does
the ratioing process automatically, so many people are almost oblivious of the quality or
otherwise of the background. However, the details of the background have a profound effect
on the quality of the spectra we record, particularly if we are making quantitative
measurements or are trying to measure very weak absorptions. The most persistent problem
is water absorption. If a ratioing process is to be meaningful, the instrument background must be invariant, it must not change to any significant degree between its acquisition and recording the spectrum of the sample, otherwise any differences will appear as positive or negative spurious bands. Most instruments, and particularly the lower cost routine ones, have sealed interferometers and sources and the sealed volume is desiccated. The sample area and the detector compartment are usually left open to the atmosphere. In these cases, the idea is that most of the optical path is relatively unattenuated by water vapour, whilst the bit that goes through the sample area and on to the detector is heavily absorbed but to a constant level (set by the level of water vapour in the lab). The problem with this approach is that, particularly at the higher resolutions (2 or 1cm-1 or better*), the attenuation can be very severe even in air conditioned labs and hence if the bands of interest lie within the envelope of the water absorption, we have severe problems with quantitative measurements. *The apparent band intensities increase as the resolution is improved. For details see Edition III, where we will publish an article by W. F. Maddams. To solve these problems, all instruments are provided with facilities to purge with dry gas (dried air or liquid nitrogen blow-off are both popular). The dry gas is normally passed through both the interferometer box and the sample and detector areas. We do this at Southampton using air dried from a commercial recycling molecular sieve system. Assuming the instrument is purged overnight, we would then expect to see an almost perfectly water-free background in the morning. Opening the sample area to introduce a specimen will, of course, contaminate the optical path with laboratory and hence wet air, but we are assured by the instrument makers that purging for a few minutes will 'sweep away' the water vapour and restore perfection to the background. There are two snags with this approach:
We have suspected for some time that the air we use here at Southampton to purge our instruments is not very dry but we have no adequate method of measuring the water level. What WE regard as a "satisfactory" background after overnight drying may well be poor. To check, we have contacted other laboratories but found some would accept our background and others would not, hence there is no real standard to which we can all aim. I therefore asked our hard-pressed Editorial Advisory Board for their help. I asked them to dry their instruments overnight using their normal routine and then run backgrounds at 1, 2 and 4cm-1 resolution, before opening the instrument sample area. The outcome is very interesting. We had several responses and the range of level of water vapour absorption was vast. Presumably people are happy with their arrangements, so the obvious question to ask is why? Presumably because they know no better! The instrument at DSM Research gave the most outstanding results. If
purged overnight, it shows no sign of bands on a full range display at 4cm-1
and about 2% at worst at 2cm-1 resolution. At 1cm-1 the water vapour bands can be discerned and peak at around
3%. Our instruments at Southampton (and we have several operating off the same supply) show peak absorptions near 1600cm-1 of at least 30% at 1cm-1 resolution on a good day! Thus, our air supply must be rubbish. If your gas supply is really dry (and DSM use nitrogen blow-off through a round-the-building manifold) you should see almost no absorption at 2cm-1. If you do, your gas supply is wet. Your water level may only be a few p.p.m. but clearly you can do better. The folks at the Malaysian Rubber Producers Research Association produce a background inferior to the D.S.M. setup, so their gas (in this case nitrogen) is not quite as dry as it could be. At 1cm-1 resolution, purged overnight at 1.5l/min gives a strongest water vapour band of around 13%. At 4cm-1 resolution and the same flushing rate, the lid was opened and a sample introduced. The CO2 absorption near 2300cm-1 once the lid was closed was ~35% and the strongest water line around 1600cm-1 about the same. Backgrounds were then recorded after 5,10,15,20,40,50 and 60 mins flushing. The last background shows the CO2 level down to about 2%, but the water is more persistent at nearer 10%. The really important point here is - the intensity of the bands changes significantly between 20 and 40 mins purging but not thereafter. The lesson is clear; once the sample compartment is opened you must purge for a long time if you are to regenerate your background quality. If you do not, you will contaminate your spectra. My account above is only an opener; in the next edition, as promised, we will run an article by Bill Maddams looking at the problem in more detail. There are a number of experimental ruses for minimising the problem and we will cover these too in the next edition. Thanks are due to Dr. Sjaak Bremmers at D.S.M. in Geleen, Holland and to Dr. Kevin
Jackson of the Malaysian Rubber Producers Research Association at Breckendonbury in the
U.K. 4. The Atmosphere Editor All of us are conscious of atmospheric absorption, our background spectra clearly showing bands around 3000 + 1650 cm-1 due to water and there are the familiar 2300 + 670 cm-1 features due to CO2. Oldies like me can remember when the background (or as we called them then - single beam runs) showed really strong absorption at shorter wavelengths. Modern FTs show them less seriously because the beam splitter restricts transmission at 3000 and higher cm-1. My point is that water vapour is THE absorber with CO2 a minor secondary feature. As a result, I have always found it difficult to follow the correlation between CO2 generation from burning fossil fuel and its contribution to global warming. I note that around 10,000 years ago the glacial icecap in Canada extended south almost to Lake Superior. By the time of Christ the cap had vanished northwards by a couple of thousand miles, but no-one burned oil or coal in this period. Is it not the case that the earth is simply warming of its own accord and will eventually start cooling again? Recently, Spectrochimica Acta has carried a correspondence between Drs. Braterman and
Barrett on global warming, a correspondence worthy of a quality scientific journal,
incomprehensible to all bar the specialist! I therefore asked Jack Barrett to write all of
us a piece explaining the role of CO2 in global warming.
He kindly and enthusiastically agreed and his article is below 5. The Spectroscopic Contributions of C02 to the Warming and Cooling of the Earth's Atmosphere Jack Barrett European Science & Environment Forum, 6 Garden Royal, Kersfield Road, London SW15 3HE. Abstract An account of some doubts about the attempts to predict climate change as the result of anthropogenic emissions of carbon dioxide. Introduction Although many factors, some still not fully understood, affect the temperature of the Earth and its atmosphere, the Intergovernmental Panel on Climate Change (IPCC) [1a] asserts that 'the body of statistical evidence...now points towards a discernible human influence on global climate.' Some scientists disagree with the methods and conclusions of the IPCC, but their criticisms are rejected by members of the IPCC and its associates [2] who claim to take notice only of professional climatologists. As one outsider (not beyond criticism [3]), the author outlines some criticisms of the IPCC attempts to find a causal link between anthropogenic emissions of CO2 and climate change. Three aspects of the problem are discussed; the experimental observations, the theoretical attempt to implicate changes in atmospheric CO2 concentrations in climate change, and a philosophical reminder of scientific method and its potentialities. Discussion Experimental observations Using Pettenkofer's method, [4] Roscoe and Schorlemmer [5] reported that the CO2 content of the air in Manchester in 1873 was 285 ppmv. Since then the concentration of the gas has increased steadily and has been determined continuously at the Mauna Loa observatory in Hawaii from 1958. The current concentration is ~366 ppmv, representing a 28% increase over 125 years that is generally regarded as being caused mainly by the oxidation of fossil fuels. The mean temperature of the Earth's surface, as estimated from a varying number of weather stations with an unrepresentative geographical distribution and from measurements taken randomly by ships, has increased over the last 100 years by between 0.3-0.6 °C (0.1-0.2%) [1b], an amount which is regarded by the IPCC as significant. Much more representative and accurate measurements of the Earth's temperature have been made continuously since 1978 by NASA satellites [6] and show zero trend to date, the variations from the mean being in the range of ?0.5 °C with variations of such a magnitude occurring sometimes over a two-week period. Since 1978 the CO2 concentration has increased by 10% with no apparent effect on the Earth's surface temperature.
Warming and cooling of the Earth's surface The predictions [1c] of the IPCC are based upon theoretical principles which have been suitably parameterized to make computer calculations possible. The atmosphere is in a quasi-equilibrium state, the solar energy received by the Earth being balanced by the emission of the same amount of energy into space over long time periods. The Sun emits broad spectrum radiation typical of its temperature, an average flux of 235 W m-2 [1d] causing heating of the Earth's atmosphere (28%) and its surface (72%). Four percent of the absorbed solar radiation is absorbed by the stratosphere where it maintains the ozone layer and another 24% is absorbed by the constituents of the lower atmosphere, including water molecules, carbon dioxide, clouds and other aerosols (i.e. smaller aggregations of water molecules which may also contain dissolved substances such as sulfur dioxide and sulfuric acid) and causes warming. Since the mean temperature of the atmosphere is lower than that of the Earth's surface there is a resultant radiative transfer of energy from the surface to the atmosphere (26 W m-2) in addition to some heat transfer (24 W m-2) and the transfer of latent heat of evaporation of water (78 W m-2), the three warming mechanisms contributing to respective extents of 20%, 19% and 61%. Of the infra-red radiation emitted by the surface, a small fraction (10%) escapes directly into space through the spectroscopic 'window' between 800-1300 cm-1; the region where none of the atmospheric constituents absorbs much energy. The remainder of the radiation is absorbed virtually completely by the water and CO2 in the lower part of the atmosphere [7]. Although CO2 absorbs strongly in the infra-red region, water molecules (particularly in their condensed phases, liquid and solid) absorb much more strongly and over a much broader frequency range. Calculations [8] using the HITRAN simulation programme [9] show that 100 m path of a typical mixture containing 36 Pa partial pressure of CO2 and the equivalent of 50% saturated water vapour (785 Pa) absorbs 72.8% of the radiation emitted by the Earth's surface. Doubling the partial pressure of CO2 causes an increase in absorption to 73.5%, an indication of the extent to which the CO2 contribution is near saturation level, due to its absorption coefficient and the considerable overlap of the CO2 0 1 bend and the rotational transitions of water molecules. It is generally agreed [10] that the extent of global warming is not determined by the initial absorption of the surface radiation, but is dependent upon the rate of cooling of the atmosphere as influenced by the level of CO2 as radiation is directed outwards with a total flux of 235 W m-2. There are arguments [11] which indicate that the warming of the lower troposphere, i.e. the lower 5 km, is caused mainly by convection and that any alteration in the rate of cooling at a higher level might not affect the temperature of the surface. Such arguments are noted by the IPCC [1e], but not refuted. The IPCC has calculated the emission characteristics of CO2 and other 'radiative' molecules by modifying the Planck function by the absorption coefficient of the species for all frequencies of interest rather than using calculated transition probabilities. The estimations of absorption coefficients are calculated from experimental values which are modified to apply to the given conditions of temperature and pressure of the upper atmosphere using the theory of line broadening [12]. The estimations are parameterized against experimental measurements, but must be subject to substantial uncertainties because of the extremes of extrapolation employed. The IPCC calculate that a doubling of the CO2 level (an eventuality which is virtually impossible even if all the fossil fuel resources were to be oxidized) will reduce the outgoing flux by ~4.4 W m-2 (1.9%) and cause global warming of about 2.8°C. It is argued [10] that the extra CO2 will allow radiation to escape from the top of the atmosphere at a higher level where the temperature is lower. The ensuing reduction in outgoing flux upsets the energy balance which must be restored by global warming, the warmer atmosphere again having the capability of emitting the required extra ~4.4 W m-1 of energy flux. There is a possibility that this argument is faulty in that the presence of more CO2 molecules offsets the effect of the lower temperature of emission, thus maintaining the energy balance.
To put the whole problem into perspective it should be realized that the heat content of the atmosphere is 1.26 x 1024 J and that over a 24 hour period the Earth's surface receives and loses about 1.06 x 1022 J or 0.8% of the atmospheric heat content. The IPCC is trying to find the effect of a change of 1.9% of that 0.8%, i.e. a change of 0.015% in the total heat content, a goal which might be beyond its capabilities. Hoyle [13] has pointed out that the fraction of solar radiation, reflected from the Earth's system, i.e. its albedo, ~30%, is not known to the degree of accuracy which would justify the sophisticated computer modelling exercises currently being carried out by the IPCC. In its annual elliptical journey around the Sun, the Earth receives an influx of radiation varying between 225 and 257 W m-2, an annual variation of 32 W m-2 which is eight times greater than the supposed effect of doubling the atmospheric CO2. When the Earth is at its nearest point to the Sun the global lower tropospheric temperature is lower by 1.8°C than when the Earth is at its farthest distance from the Sun [14]. Such an observation is a possible indication of the operation of an Earth thermostat mechanism which would cast doubt upon whether the IPCC derived alteration of ~4.4 W m-2 in the radiation flux is a potential factor which might lead to climate change. Scientific method As a final point it should be pointed out that whatever changes occur to the climate in future years, and whatever actions humans take to try to modify such changes, will be beyond scientific analysis because we will never know what changes would have occurred had we not taken such actions. [1] Houghton, J.T., Meira Filho, L.G., Callander, B.A., Harris, N., Kattenberg, A., & Maskell, K., (eds), Climate Change 1995, Cambridge University Press, (a) p. 438, (b) p. 26, (c) p. 39, (1d) p. 58, (1e) p. 200, (1996). [2] Harries, J. E., & Slingo, A., personal communications, NERC seminar meeting, Nottingham, (1996). [3] See for example, Braterman, P., Spectrochimica Acta, 52A, (1996), 1565 and the reply, Barrett, J., ibid., 52A, (1996), 1567. [4] Pettenkofer, M., J. Chem. Soc., (1858), 292. [5] Roscoe, H. E., & Schorlemmer, C., A Treatise on Chemistry, MacMillan & Co., London, (1905), p. 591. [6] Spencer, R. W., and Christy, J. R., 1994. Global and hemispheric and stratospheric temperature anomalies from satellite records. pp. 629-634. In T. A. Boden, D. P. Kaiser, R. J. Sepanski, and F.W. Stoss (eds.), Trends '93: A Compendium of Data on Global Change. ORNL/CDIAC-65. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tenn., U.S.A. [7] McIlveen, R., Fundamentals of Weather and Climate, Chapman & Hall, p. 251, (1992). [8] Barrett, J., Treibhaus-kontroverse und Ozon-problem, Symposium der Europaischen Akademie fur Umweltfragen, H. Metzner, (ed.), Leipzig, (1996), p.169. [9] HITRAN-PC, the IBM-PC version of the HITRAN Database and User Programs, University of South Florida, Version 1.1, (1992). [10] Houghton, Sir J., Spectrochimica Acta, 51A, (1995), 1391. [11] Lindzen, R. S., Bull. Am. Met. Soc., 71, (1990), 288. [12] Houghton, J. T., Meira Filho, L. G., Bruce, J., Hoesung Lee, Callander, B.A., Haites, E., Harris, N., & Maskell, K., (eds), Climate Change 1994, Cambridge University Press, p.170, (1995). [13] Hoyle, Sir F., The Global Warming Debate, J. Emsley, ed., The European Science and Environment Forum, (1996), p. 179. [14] Christy, J. R., personal communication of 1983-1990 data; the author's analysis, (1996). REF: Int. J. Vib. Spect., [www.ijvs.com] 1,
2, 5 (1996)
Assuming Dr. Barrett is correct, one must wonder why the Establishment is so keen on blaming the combustion of coal and oil for global warming. The reason, I strongly suspect, is that utter shower - our political Lords and Masters. Hype up the CO2 yarn, a subject about which lawyers and their ilk know absolutely nothing, and hence justify "carbon taxes", increased tax on car fuel and, in the U.K., "VAT on fuel bills". Result - the gullible and scientifically illiterate (the vast majority of the electorate) will swallow this rubbish and vote as required. Pressure groups like Greenpeace can be manipulated to shout to numbers, providing free-of-charge support for the taxes and votes to boot. Or am I just a cynic? 6. Sampling in FT-Raman Spectroscopy Should one wish to follow a reaction or physical change which occurs at
low temperatures there is little alternative to cooling. P.T.F.E. is highly but not
exclusively crystalline and the crystals contain -CF2CF2-CF2- species in helical
structures. Below 19°C the helix has a different pitch from that at high temperatures and
the spectrum changes as the crystal structure alters. Or - you might wish to run the
spectrum of a solid melting below room temperature - cool, freeze and study. Raise the
temperature and follow phase changes below the melting point, raise the temperature and
melt the specimen. All this is pretty obvious stuff but students of Edition I will ask -
what about sample heating? The laser itself will raise the temperature by a variable
amount but certainly not by a trivial degree or so; the problem can be far more serious
than that. Sometimes, sample heating can be a disaster. If a transition of interest occurs
near room temperature, the bulk of the specimen can easily lie below the critical
temperature but the tiny volume illuminated by the laser can be far hotter and in fact
ABOVE the crucial value. I suggested ways of solving this problem in Edition I but in many
cases there is no alternative to cooling. Let us say a transition of interest
(freezing/melting or a crystal structure change) occurs at 10°C and laser heating might
amount to 40-50°C; the precise value we know not. In this type of case, cooling to
cryogenic temperatures will guarantee that no harm is done by the laser. So we need a cold
cell. Cold Cells In principle there are four types of cold cell suitable for Raman spectroscopy:
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and at temperatures above 150°a background always appears, due to black body
emission. Careful design to minimise pickup from the heated parts of the cell can help,
but it is very hard to record spectra much above 180°C with an FT instrument. The
background above this temperature becomes overwhelming at high shifts. In principle, one
could operate above this temperature by subtracting the background, but there are two
problems with this idea. 
