J. Marcos Sirota

Hydrogen and helium pressure broadening of water transitions in the 380– region

Abstract We present results of recent experiments on the pressure broadening of pure rotational transitions of H216O water in the 380– 600 cm −1 range by hydrogen and helium. The hydrogen coefficients vary between 0.033 and 0.076 cm −1 / atm (average: 0.056 cm −1 / atm ) while the helium coefficients vary between 0.006 and 0.017 cm −1 / atm (average: 0.013 cm −1 / atm ) . While this average hydrogen-broadening coefficient matches the average nitrogen-broadening coefficient we observed in this region earlier, the range over which they vary is narrower for hydrogen than for nitrogen. We find that previously published complex Robert–Bonamy formalism calculations of the hydrogen coefficients are broadly consistent with these results, and that, to some extent, our experimental results can be predicted from HITRAN air widths.

Pressure broadening coefficients for rotational transitions of water in the 380–600 cm−1 range

Abstract We present results of recent experiments on the pressure broadening of pure rotational transitions of H216O water in the 400– 600 cm −1 range by nitrogen and oxygen. The average broadening coefficient is about 0.056 cm −1 / atm for N2 and about 0.029 cm −1 / atm for O2, however, as expected, the broadening coefficient varies as a strong function of transition. In general, the broadening decreases with increasing J and Ka, with a stronger dependence on Ka than on J. On average, air broadening coefficients obtained from the coefficients presented here are about 10% lower than those found in HITRAN ’96, although, as detailed below, the differences are a function of quantum number.

Line strength and self-broadening coefficient of the pure rotational S(1) quadrupole line in H2

The absolute intensity, S(sub 1), and self-broadening coefficient, gamma(sub L), for H2 S(sub zero)(1) pure rotational line at 17.0348 micrometers (587.032 cm(exp -1)) have been measured for the first time using a tunable diode laser spectrometer with a resolution of approximately 1 x 10(exp -3) cm(exp -1). By fitting a Galatry line shape convolved with a 1 x 10(exp -3) cm(exp -1) Gaussian instrument profile to absorption profiles, for H2 pressures ranging from 0.34 to 1.30 atm, values of s(sub 1) = (7.0 +/- 0.4) x 10(exp -8) cm(exp -2) atm(exp -1) and gamma(sub L) = (1.73 +/- 0.12) x 10(exp -3) cm(exp -1) atm(exp -1) were obtained.

Perturbative study of spectral line shapes involving line-mixing and collision-duration asymmetry

A perturbative theory has been developed to model the spectral line shapes affected by line-mixing and finite duration-of-collision. The line profile was given in an explicit form tractable for dealing with the line interference and asymmetry problems. The coupling of line-mixing and collision-duration was studied. The simplified model was conditionally applied to the CO2 ν3 high-frequency wing beyond the bandhead, and was found to reproduce the experimental absorption coefficients well. The effective collision-duration parameters were obtained from the fit of the ν3 band edge and from the typical CO2–CO2 collision time of 1 ps. These parameters were then used to calculate the Q-branch core region of the CO2 ν2 band near 667 cm−1. The coupling effect from line-mixing and finite-duration was theoretically shown to be discernible at the pressure of 1 amagat. This effect grows with increased pressures and, expectedly, becomes significant for higher pressures.

Absolute line intensities and broadening coefficients for the ν11 band of allene

Abstract Line strengths for the ν11 band of allene (352.636 cm−1) have been measured using tunable diode laser spectroscopy. The dipole moment and band strengths have been derived, and pressure broadening coefficients for self and N2 broadening were determined at temperatures representative of Titans atmosphere (160–190 K). The absolute value for the dipole moment is 0.1093 debye giving a band intensity of 26.29 cm−2 atm−1 (300 K). This band strength is about 6% lower than that inferred from the low resolution measurements performed by Koga et al,14 which is the only previous strength measurement for this band.