Prasad Varanasi

Measurement of line widths of CO of planetary interest at low temperatures

Self-broadened, air-broadened and CO2-broadened half-widths of lines R(0) through R(0) in the CO fundamental have been measured at 100°K (self-broadening only), 200°K, 250°K and 300°K using the Ladenburg-Reiche curve-of-growth. The relation γ°m(T)γ°m(300°K)=(300T)0.75, which we found previously for the nitrogen-broadened half-widths of R(0), R(8) and R(16), is shown to be valid for all of the line widths measured in the present study.

Absorption coefficients for water vapor in the 600–1000 cm-1 region

Abstract Experimental determinations of absorption coefficients of water vapor are presented for temperatures between 400 and 500°K and pressures of 2 and 10 atm. All measurements were made by using the technique of self-broadening, moderate resolution (≈ 25 cm -1 ), and a supply source of liquid water at variable temperatures. The observed results are consistent with the idea that hydrogen bonding contributes to the absorption coefficient of water vapor in the spectral region between 600 and 1000 cm -1 .

Measurements of intensities and nitrogen-broadened linewidths in the CO fundamental at low temperatures

Intensities and nitrogen-broadened half-widths of lines R (0), R (8) and R (t6) in the fundamental band of ~2C60 have been measured at 83°K, 100°K, 150*K, 200°K and 298°K. The intensities of several other lines in the P- and R-branches of the band have also been measured at 298°K. The absolute intensity derived from the line intensity data using the Herman-Wallis formula is SO = 273 -+ 10 cm -2 atm -t at S.T.P. A separate measurement employing the Wilson-Wells--Penner-Weber method has yielded S°~ = 277-+ 4 cm -2 atm -~ at S.T.P. Both of these values are within 6 per cent of most of the previously published direct measurements of this parameter. The values for the line intensities reported earlier by other authors are lower by nearly 16 per cent.

Shapes and widths of ammonia lines collision-broadened by hydrogen.

Abstract Half-widths and shapes of several rotational lines in v 2 -bands of ammonia, collision-broadened by hydrogen, have been measured, at room temperature, with a spectral resolution of 0.15 cm -1 . Line intensities and self-broadened half-widths have also been measured. From the line-intensity data, an estimate of S band = 600±30 cm -2 atm -1 has been derived for the absolute intensity of the pair of bands. Hydrogen-broadened half-widths of all the lines have been found to be equal to 0.075±0.004 cm -1 atm -1 . For all the lines measured, shapes of the lines in NH 3 -H 2 collisions seem to conform to the super-Lorentz line shape proposed by Varanasi et al. for dipole-quadrupole collisions.

Collision-broadened half-widths and shapes of methane lines☆

Abstract High-resolution measurements are reported on a few rotational lines in the ν3-fundamental and the 2ν3-overtone of methane. Half-width data are presented in self-broadening and in broadening by H2, He, N2, O2 and air. Comparison with available data on 3ν3-band shows, within experimental error, that the line-widths are the same for ν3 and its overtones in all cases of broadening. The half-widths exhibit an observable dependence on the rotational quantum number only in self-broadening and nitrogen-(and air-) broadening. Line-shape measurements in the ν3-fundamental suggest that the Lorentz contour for collision-broadened lines in an accurate representation for all cases of broadening that were studied.

Intensity and half-width measurements in the 1·525 μm band of acetylene☆

Line intensities at 150°K and 295°K, self-broadened half-widths at 171°K, 200°K, 250°K and 295°K, and hydrogen-broadened half-widths at 171°K, 200°K and 295°K have been measured in the ν1+v3 band of C2H2 at 1·525 μm. The absolute intensity of the band has been determined independently by employing the Wilson-Wells-Penner-Weber technique. Our best estimate for the absolute intensity of the band is Sv=7·82 ± 0·07 cm−2 atm−1 at 295°K. Line intensities calculated using this value of Sv are in good agreement with the measured intensities at the two extreme temperatures of 150°K and 295°K considered in the present study, thereby not suggesting any significant intensity anomalies. Line positions have been measured for the first time for this band for R(29)−P(25).

Experimental and theoretical studies on collision-broadened lines in the v4-fundamental of methane☆

Abstract High-resolution experimental and theoretical studies performed earlier by us on the collision-broadened rotational lines in the v 3 - and 2 v 3 -bands of methane have been repeated on the lines in the v 4 -fundamental of the molecule. Line-width measurements and computations, as well as line-shape measurements, indicate that the significant differences which exist between the rotational term values of the v 3 -type and v 4 -type vibrational levels have no observable effect on the collision-broadening mechanism. Using the predictions of line-widths, based on the Anderson-Tsao-Curnutte theory in the extended version of Tejwani for octopolar molecules, the theoretical dependence of line-widths on temperature has been calculated for CH 4 -CH 4 , CH 4 -H 2 and CH 4 -He collisions.

Line shape parameters for HCl and HF in a CO2 atmosphere.

Abstract High-resolution (0.1 cm−1) measurements have been performed on several CO2-broadened lines in the fundamentals of HCl35 and HCl37. Line intensities, half-widths and shapes have been determined at room temperature. Half-widths in HCl-CO2 and HF-CO2 collisions have been computed for several temperatures employing Andersons theory. The measured shapes of HCl lines broadened by CO2 are described by a semi-empirical super-Lorentzian line shape, given by K ν = S πγ ƞ 2 sin π ƞ |ν−ν 0 γ ƞ +1 −1 with ƞ = 1.75 . The curve-of-growth for this line shape has been derived in terms of a function similar to the Ladenburg-Reiche function. Absorption between R(0) and P(1) is affected by the appearance of several pressure-induced Q-branch lines, at the pressures from one to ten atmospheres used in the present study.

Intensity measurements in freon bands of atmospheric interest

The absolute intensities of the i.r. absorption bands, which are located in the atmospheric window region, of CFCl3 (“Freon-11”) and CF2Cl2 (“Freon-12”) have been measured at 300°K. Our best estimates for these parameters are: for CFCl3 (“Freon-11”), Sv = 635±36 cm-2atm-1 (9.2μ band), Sv = 1536±45 cm-2atm-1 (11.8μ band); for CF2Cl2 (“Freon-12”), Sv = 718±14 cm-2atm-1 (8.7μ band), Sv = 1136±22 cm-2atm-1 (9.1μ band), and Sv = 1302±40 cm-2atm-1 (10.9μ band).

Collision-broadened linewidths of tetrahedral molecules—II. Computations for CH4 lines broadened by N2, O2, He, Ne and Ar☆

Pressure-broadened widths of CH4 lines have been calculated, using the recent formulation for tetrahedral molecules by Varanasi in the framework of the Anderson-Tsao-Curnutte theory. The present work deals mainly with lines of the R-branch of the ν3-fundamental at 300°K, for the range 1≤J≤30 and 0≤K≤18, and for the F species. In the case of CH4-N2 and CH4-O2 collisions, octopole-quadrupole, octopole-hexadecapole, hexadecapole-quadrupole, hexadecapole-hexadecapole, dispersion and overlap interactions have been included. Broadening by noble gases was treated in terms of dispersion and overlap interactions. The value |ΩCH4|=2·25×10−34 esu cm3 obtained in the present work by comparing theoretical and experimental results for γ0CH4−N2 is not far from the magnitude deduced in studies of the far-i.r. collision-induced absorption spectra of methane. A magnitude for the hexadecapole moment of |ΦCH4|=3·0×10−42 esu cm4 was also determined. The calculated and measured linewidths are in good agreement, except in CH4-Ar collisions. In the latter case, the theoretical values are appreciably lower than the experimental ones, which suggests that induced interactions may have to be included.