1
|
Galanina TA, Koroleva AO, Amerkhanov IS, Serov EA, Koshelev MA, Tretyakov MY, Chistikov DN, Finenko AA, Vigasin AA. On the nature of sub-THz continuum absorption in CO 2 gas, its mixture with Ar, and in pure water vapor. Phys Chem Chem Phys 2024; 26:15032-15043. [PMID: 38742911 DOI: 10.1039/d4cp00240g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
Detailed analysis of the unique broadband millimeter-wave (70-360 GHz) collision-induced absorption spectra in pure CO2 and in its mixture with Ar is presented. The nature of the observed continuum absorption is examined using classical trajectory simulation along with statistical physics consideration. Bimolecular continuum is decomposed in the phase space into separate contributions from the so-called free, quasibound, and true bound molecular pairs, the proportions of which greatly vary with temperature. This partitioning is supported by consideration of the second virial coefficient and excluded volume in pure CO2, Ar, and CO2-Ar. Close similarity between collision-induced absorption in the CO2 containing gases and the water vapor continuum in the subterahertz spectral range is demonstrated. This similarity suggests that the physical principles underlying both continuum absorption phenomena have much in common and, therefore, can be used for continuum modeling.
Collapse
Affiliation(s)
- T A Galanina
- A. V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov str., Nyzhny Novgorod 603950, Russia.
| | - A O Koroleva
- A. V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov str., Nyzhny Novgorod 603950, Russia.
| | - I S Amerkhanov
- A. V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov str., Nyzhny Novgorod 603950, Russia.
| | - E A Serov
- A. V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov str., Nyzhny Novgorod 603950, Russia.
| | - M A Koshelev
- A. V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov str., Nyzhny Novgorod 603950, Russia.
| | - M Yu Tretyakov
- A. V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov str., Nyzhny Novgorod 603950, Russia.
| | - D N Chistikov
- A. V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov str., Nyzhny Novgorod 603950, Russia.
- A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, 3 Pyzhevsky Per., Moscow 119017, Russia
- Department of Chemistry, Lomonosov Moscow State University, GSP-1, 1-3 Leninskiye Gory, Moscow 119991, Russia
- Institute of Quantum Physics, Irkutsk National Research Technical University, 83 Lermontov str., Irkutsk 664074, Russia
| | - A A Finenko
- A. V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov str., Nyzhny Novgorod 603950, Russia.
- Department of Chemistry, Lomonosov Moscow State University, GSP-1, 1-3 Leninskiye Gory, Moscow 119991, Russia
- Institute of Quantum Physics, Irkutsk National Research Technical University, 83 Lermontov str., Irkutsk 664074, Russia
| | - A A Vigasin
- A. V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences, 46 Ulyanov str., Nyzhny Novgorod 603950, Russia.
- A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, 3 Pyzhevsky Per., Moscow 119017, Russia
| |
Collapse
|
2
|
Vogt E, Simkó I, Császár AG, Kjaergaard HG. Quantum Chemical Investigation of the Cold Water Dimer Spectrum in the First OH-Stretching Overtone Region Provides a New Interpretation. J Phys Chem A 2023; 127:9409-9418. [PMID: 37930939 DOI: 10.1021/acs.jpca.3c03705] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2023]
Abstract
Intramolecular vibrational transition wavenumbers and intensities were calculated in the fundamental HOH-bending, fundamental OH-stretching, first OH-stretching-HOH-bending combination, and first OH-stretching overtone (ΔvOH = 2) regions of the water dimer's spectrum. Furthermore, the rotational-vibrational spectrum was calculated in the ΔvOH = 2 region at 10 K, corresponding to the temperature of the existing jet-expansion experiments. The calculated spectrum was obtained by combining results from a full-dimensional (12D) vibrational and a reduced-dimensional vibrational-rotational-tunneling model. The ΔvOH = 2 spectral region is rich in features due to contributions from multiple vibrational-rotational-tunneling sub-bands. Origins of the experimental vibrational bands depend on the assignment of the observed sub-bands. Based on our calculations, we assign the observed sub-bands, and our reassignment leads to new values for the vibrational band origins of the free donor and antisymmetric acceptor OH-stretching first overtones of ∼7227 and ∼7238 cm-1, respectively. The observed bands with origins at 7192.34 and ∼7366 cm-1 are assigned to the symmetric acceptor OH-stretching first overtone and the OH-stretching combination of the donor, respectively.
Collapse
Affiliation(s)
- Emil Vogt
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, Copenhagen Ø DK-2100, Denmark
| | - Irén Simkó
- Laboratory of Molecular Structure and Dynamics, Institute of Chemistry ELTE Eötvös Loránd University, Pázmány Péter Sétány 1/A, Budapest H-1117, Hungary
- HUN-REN-ELTE Complex Chemical Systems Research Group, P.O. Box 32, Budapest 112 H-1518, Hungary
| | - Attila G Császár
- Laboratory of Molecular Structure and Dynamics, Institute of Chemistry ELTE Eötvös Loránd University, Pázmány Péter Sétány 1/A, Budapest H-1117, Hungary
- HUN-REN-ELTE Complex Chemical Systems Research Group, P.O. Box 32, Budapest 112 H-1518, Hungary
| | - Henrik G Kjaergaard
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, Copenhagen Ø DK-2100, Denmark
| |
Collapse
|
3
|
Sitha S. Ortho-para interconversion of nuclear states of H 2O through replica transition state: prospect of quantum entanglement at homodromic Bjerrum defect site. J Mol Model 2023; 29:242. [PMID: 37436555 PMCID: PMC10338397 DOI: 10.1007/s00894-023-05646-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Accepted: 07/01/2023] [Indexed: 07/13/2023]
Abstract
CONTEXT From a nuclear spin prospective, water exists as para and ortho nuclear spin isomers (isotopomers). Spin interconversions in isolated molecules of water are forbidden, but many recent reports have shown them to happen in bulk, through dynamic proton exchanges happening between interconnected networks of a large array of water molecules. In this contribution, a possible explanation for an unexpected slow or delayed interconversion of ortho-para water in ice observed in an earlier reported experiment is provided. Using the results of quantum mechanical investigations, we have discussed the roles played by Bjerrum defects in the dynamic proton exchanges and ortho-para spin state interconversions. We guess that at the sites of the Bjerrum defects, there are possibilities of quantum entanglements of states, through pairwise interactions. Based on the perfectly correlated exchange happening via a replica transition state, we speculate that it can have significant influences on ortho-para interconversions of water. We also conjecture that the overall ortho-para interconversion is not a continuous process, rather can be imagined to be happening serendipitously, but within the boundary of the rules of quantum mechanics. METHODS All computations were performed with Gaussian 09 program. B3LYP/6-31++G(d,p) methodology was used to compute all the stationary points. Further energy corrections were computed using CCSD(T)/aug-cc-pVTZ methodology. Intrinsic reaction coordinate (IRC) path computations were carried out for the transition states.
Collapse
Affiliation(s)
- Sanyasi Sitha
- Department of Chemical Sciences, APK Campus, University of Johannesburg, PO Box 524, Auckland Park, Johannesburg, 2006, South Africa.
| |
Collapse
|
4
|
Vogt E, Kjaergaard HG. Vibrational Spectroscopy of the Water Dimer at Jet-Cooled and Atmospheric Temperatures. Annu Rev Phys Chem 2022; 73:209-231. [PMID: 35044791 DOI: 10.1146/annurev-physchem-082720-104659] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The vibrational spectroscopy of the water dimer provides an understanding of basic hydrogen bonding in water clusters, and with about one water dimer for every 1,000 water molecules, it plays a critical role in atmospheric science. Here, we review how the experimental and theoretical progress of the past decades has improved our understanding of water dimer vibrational spectroscopy under both cold and warm conditions. We focus on the intramolecular OH-stretching transitions of the donor unit, because these are the ones mostly affected by dimer formation and because their assignment has proven a challenge. We review cold experimental results from early matrix isolation to recent mass-selected jet expansion techniques and, in parallel, the improvements in the theoretical anharmonic models. We discuss and illustrate changes in the vibrational spectra of complexes upon increasing temperature, and the difficulties in recording and calculating these spectra. In the atmosphere, water dimer spectra at ambient temperature are crucial. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 73 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Collapse
Affiliation(s)
- Emil Vogt
- Department of Chemistry, University of Copenhagen, Copenhagen, Denmark;
| | | |
Collapse
|
5
|
Odintsova TA, Tretyakov MY, Simonova AA, Ptashnik IV, Pirali O, Campargue A. Measurement and temperature dependence of the water vapor self-continuum between 70 and 700 cm−1. J Mol Struct 2020. [DOI: 10.1016/j.molstruc.2020.128046] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
|
6
|
|
7
|
Odintsova T, Tretyakov M, Zibarova A, Pirali O, Roy P, Campargue A. Far IR continuum absorption of H 216O and H 218O. EPJ WEB OF CONFERENCES 2018. [DOI: 10.1051/epjconf/201819506011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
8
|
Serov EA, Koshelev MA, Odintsova TA, Parshin VV, Tretyakov MY. Rotationally resolved water dimer spectra in atmospheric air and pure water vapour in the 188–258 GHz range. Phys Chem Chem Phys 2014; 16:26221-33. [DOI: 10.1039/c4cp03252g] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Millimeter wave spectra of the water dimer under the conditions close to the atmospheric ones in pure water vapour and its mixture with air are detected and quantitatively analyzed.
Collapse
Affiliation(s)
- E. A. Serov
- Institute of Applied Physics of the Russian Academy of Sciences
- 46 Ul'yanov str
- Nizhny Novgorod, Russian Federation
| | - M. A. Koshelev
- Institute of Applied Physics of the Russian Academy of Sciences
- 46 Ul'yanov str
- Nizhny Novgorod, Russian Federation
| | - T. A. Odintsova
- Institute of Applied Physics of the Russian Academy of Sciences
- 46 Ul'yanov str
- Nizhny Novgorod, Russian Federation
| | - V. V. Parshin
- Institute of Applied Physics of the Russian Academy of Sciences
- 46 Ul'yanov str
- Nizhny Novgorod, Russian Federation
| | - M. Yu. Tretyakov
- Institute of Applied Physics of the Russian Academy of Sciences
- 46 Ul'yanov str
- Nizhny Novgorod, Russian Federation
| |
Collapse
|
9
|
Affiliation(s)
- Branko Ruscic
- Chemical
Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States, and Computation Institute, University of Chicago, Chicago, Illinois 60637, United
States
| |
Collapse
|
10
|
Tretyakov MY, Serov EA, Koshelev MA, Parshin VV, Krupnov AF. Water dimer rotationally resolved millimeter-wave spectrum observation at room temperature. PHYSICAL REVIEW LETTERS 2013; 110:093001. [PMID: 23496706 DOI: 10.1103/physrevlett.110.093001] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2012] [Indexed: 06/01/2023]
Abstract
Water dimers (H(2)O)(2) are believed to affect Earth's radiation balance and climate, homogeneous condensation, and atmospheric chemistry. Moreover, the pairwise interaction which binds the dimer appears to be of paramount importance for expounding a complete molecular description of the liquid and solid phases of water. However, there have been no secure, direct observations of water dimers at environmentally relevant temperatures despite decades of studies. We report the first unambiguous observation of the dimer spectrum recorded in equilibrium water vapor at room temperature.
Collapse
Affiliation(s)
- M Yu Tretyakov
- Institute of Applied Physics, Russian Academy of Sciences, 46 Ulyanov Street, Nizhny Novgorod, Russia 603950.
| | | | | | | | | |
Collapse
|
11
|
|
12
|
Tennyson J, Barber MJ, Kelly REA. An adiabatic model for calculating overtone spectra of dimers such as (H(2)O)(2). PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2012; 370:2656-2674. [PMID: 22547237 DOI: 10.1098/rsta.2011.0243] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The near-infrared and visible wavelength spectrum of the water dimer is considered to be the major contributor to the so-called water continuum at these wavelengths. However, theoretical models of this spectrum require the simultaneous treatment of both monomer and dimer excitations. A model for treating this problem is proposed which is based upon a Franck-Condon-like separation between the monomer and dimer vibrational motions. In this model, one of the monomers is treated as the chromophore and its absorption is assumed to be given by its, possibly perturbed, vibrational band intensity. The main computational issue is the treatment of separate monomer and dimer motions. Various approaches for obtaining dimer vibration-rotation tunnelling spectra that allow for monomer motion are explored. These approaches include ways of treating the adiabatic separation of dimer vibrational modes from monomer vibrational modes. We classify the adiabatic separation methods under four main approaches: namely fixed-geometry, free-monomer, perturbed-monomer and coupled-monomer methods. The latter being the most computationally expensive as the monomer wave functions are dependent on the dimer coordinates. For each of these approaches, expectation values over the full potential are calculated for the given monomer vibrational wave functions. Various full (named VAP 2pD in the text) and partial (VAP (+p)D) averaging techniques are outlined to calculate the vibrationally averaged, monomer state-dependent, dimer interaction potentials. The computational costs associated with application of these techniques to the water dimer are estimated and the prospects for full calculations based on this approach are assessed.
Collapse
Affiliation(s)
- J Tennyson
- Department of Physics and Astronomy, University College London, London WC1E 6BT, UK.
| | | | | |
Collapse
|
13
|
Turner DD, Merrelli A, Vimont D, Mlawer EJ. Impact of modifying the longwave water vapor continuum absorption model on community Earth system model simulations. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011jd016440] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
14
|
Thomsen DL, Kurtén T, Jørgensen S, Wallington TJ, Baggesen SB, Aalling C, Kjaergaard HG. On the possible catalysis by single water molecules of gas-phase hydrogen abstraction reactions by OH radicals. Phys Chem Chem Phys 2012; 14:12992-9. [DOI: 10.1039/c2cp40795g] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
|
15
|
Ptashnik IV, McPheat RA, Shine KP, Smith KM, Williams RG. Water vapor self-continuum absorption in near-infrared windows derived from laboratory measurements. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011jd015603] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
|
16
|
Tretyakov MY, Makarov DS. Some consequences of high temperature water vapor spectroscopy: water dimer at equilibrium. J Chem Phys 2011; 134:084306. [PMID: 21361538 DOI: 10.1063/1.3556606] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
It is shown that the evolution of water vapor spectra in the 2500-5000 cm(-1) range recorded at 650 K and pressures up to 130 atms after subtraction of monomer contribution may be interpreted qualitatively well on the basis of experimental data on water dimer and trimer obtained from cold molecular beams and in He droplets. The proposed spectroscopic model considers water vapor as a mixture of nonideal monomers, dimers, and trimers at chemical equilibrium. The effect of line mixing is taken into account in the monomer spectrum modeling. Decomposition of the high temperature spectra allowed determining a dimer equilibrium constant that was compared with the previously known values. The contribution of water trimer is assessed. The performed analysis indicates that the number of bound dimers in water vapor is quite large, even at such a high temperature.
Collapse
Affiliation(s)
- M Yu Tretyakov
- Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia.
| | | |
Collapse
|
17
|
Wang XG, Carrington T. Theoretical study of the rovibrational spectrum of H2O–H2. J Chem Phys 2011; 134:044313. [DOI: 10.1063/1.3533230] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
18
|
Xue Z, Suhm MA. Adding more weight to a molecular recognition unit: the low-frequency modes of carboxylic acid dimers. Mol Phys 2010. [DOI: 10.1080/00268976.2010.508600] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
|
19
|
Bégué D, Baraille I, Garrain PA, Dargelos A, Tassaing T. Calculation of IR frequencies and intensities in electrical and mechanical anharmonicity approximations: Application to small water clusters. J Chem Phys 2010; 133:034102. [DOI: 10.1063/1.3457482] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
20
|
Leforestier C, Tipping RH, Ma Q. Temperature dependences of mechanisms responsible for the water-vapor continuum absorption. II. Dimers and collision-induced absorption. J Chem Phys 2010; 132:164302. [DOI: 10.1063/1.3384653] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- C Leforestier
- Institut Charles Gerhardt CNRS-5253, CC15.01, Université Montpellier 2, 34095 Montpellier, France
| | | | | |
Collapse
|
21
|
Shank A, Wang Y, Kaledin A, Braams BJ, Bowman JM. Accurate ab initio and “hybrid” potential energy surfaces, intramolecular vibrational energies, and classical ir spectrum of the water dimer. J Chem Phys 2009; 130:144314. [DOI: 10.1063/1.3112403] [Citation(s) in RCA: 146] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
|
22
|
Lee MS, Baletto F, Kanhere DG, Scandolo S. Far-infrared absorption of water clusters by first-principles molecular dynamics. J Chem Phys 2008; 128:214506. [PMID: 18537432 DOI: 10.1063/1.2933248] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Based on first-principle molecular dynamic simulations, we calculate the far-infrared spectra of small water clusters (H(2)O)(n) (n = 2, 4, 6) at frequencies below 1000 cm(-1) and at 80 K and at atmospheric temperature (T>200 K). We find that cluster size and temperature affect the spectra significantly. The effect of the cluster size is similar to the one reported for confined water. Temperature changes not only the shape of the spectra but also the total strength of the absorption, a consequence of the complete anharmonic nature of the classical dynamics at high temperature. In particular, we find that in the frequency region up to 320 cm(-1), the absorption strength per molecule of the water dimer at 220 K is significantly larger than that of bulk liquid water, while tetramer and hexamer show bulklike strengths. However, the absorption strength of the dimer throughout the far-infrared region is too small to explain the measured vapor absorption continuum, which must therefore be dominated by other mechanisms.
Collapse
Affiliation(s)
- Mal-Soon Lee
- The Abdus Salam International Centre for Theoretical Physics, I-34014 Trieste, Italy
| | | | | | | |
Collapse
|
23
|
Ma Q, Tipping RH, Leforestier C. Temperature dependences of mechanisms responsible for the water-vapor continuum absorption. I. Far wings of allowed lines. J Chem Phys 2008; 128:124313. [PMID: 18376925 DOI: 10.1063/1.2839604] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
It is well known that the water-vapor continuum plays an important role in the radiative balance in the Earth's atmosphere. This was first discovered by Elsasser almost 70 years ago, and since that time there has been a large body of work, both experimental and theoretical, on this topic. It has been experimentally shown that for ambient atmospheric conditions, the continuum absorption scales quadratically with the H(2)O number density and has a strong, negative temperature dependence (T dependence). Over the years, there have been three different theoretical mechanisms postulated: Far wings of allowed transitions, water dimers, and collision-induced absorption. Despite the improvements in experimental data, at present there is no consensus on which mechanism is primarily responsible for the absorption. The first mechanism proposed was the accumulation of the far-wing absorption of the strong allowed transitions. Later, absorption by water dimers was proposed and this mechanism provides a qualitative explanation for the strong, negative T dependence. Recently, some atmospheric modelers have proposed that collision-induced absorption is one of the major contributors. However, based on improvements in the theoretical calculation of accurate far-wing line shapes, ab initio dimer calculations, and theoretical collision-induced absorptions, it is now generally accepted that the dominant mechanism for the absorption in the infrared (IR) windows is that due to the far wings. Whether this is true for other spectral regions is not presently established. Although all these three mechanisms have a negative T dependence, their T dependences will be characterized by individual features. To analyze the characteristics of the latter will enable one to assess their roles with more certainty. In this paper, we present a detailed study of the T dependence of the far-wing absorption mechanism. We will then compare our theoretical calculations with the most recent and accurate experimental data in the IR windows. The results of our calculations are found to agree very well with measurements in the 800-1200 cm(-1) region. We conclude from this work that the T dependence in the IR window region predicted by the far-wing theory is negative and moderately strong. Its pattern is not simple and it could vary significantly as the frequency of interest varies.
Collapse
Affiliation(s)
- Q Ma
- NASA/Goddard Institute for Space Studies and Department of Applied Physics and Applied Mathematics, Columbia University, 2880 Broadway, New York, New York 10025, USA.
| | | | | |
Collapse
|