Spectral line shape of theP(2)transition in CO-Ar: Uncorrelatedab initiocalculation

Abstract

We calculate the spectral line shape of an isolated line from first principles, assuming that the translational motion is not statistically correlated with the evolution of the optical coherence, i.e., with the broadening. We use the known, realistic potentials for the influence of collisions on the translational motion and on the internal motion. We show that the calculated profiles do not agree, particularly at low pressures, with very precise experimental profiles of the P(2) line of CO in a bath of Ar. We establish that the source of the disagreement lies in the assumption of uncorrelated effects of collisions on the translational motion and the optical coherence associated with the internal degrees of freedom.

An accurate comparison of lineshape models on H2O lines in the spectral region around 3μm

“…This may be associated with low rotational quantum number J of states corresponding to this transition (see Table 1). It was also reported by Duggan et al [16] and later confirmed by Wehr et al [53] that speed-dependent effects play more important role in case of transitions involving low than high J number states, and our simplified form of speed-dependencies is more clearly seen here than for other lines. The analysis presented above leads to a conclusion that exact speed-dependence of c L and D must be known to find reliable values of frequency of velocity changing collisions m H in the case of investigated H 2 O lines perturbed by Xe.…”

Self- and foreign-gas-broadened lineshapes in the ν1 band of NH3

“…(8), we can attribute any b m 6 b d to correlation between velocity-changing and dephasing collisions [3]. Here, only the self-collisions yield b m > b d , which is normally a signal of speed-dependent broadening [8,11,25]. When speeddependent broadening is included for the sdR profile, the Dicke-narrowing coefficients show a drastic reduction for the foreign-gas cases, but an unusual increase for self-collisions.…”

“…Ideally, the speed dependence of the broadenings and shifts can be calculated either semiclassically or quantum-mechanically from realistic interaction potentials. However, this has been done for only a few simple cases such as HF-Ar [23,24] and CO-Ar [25]. Therefore, we use the classical-path R Àq potential model of Berman [9] and Ward et al [10].…”

Self-broadened 12C16O line shapes in the v=2←0 band

“…These effects have been observed for CO line shapes in a number of high-resolution studies [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], motivated in part by the need to monitor this species accurately in the earth and planetary atmospheres. Most of the CO line shape measurements have been reported for the v ¼ 1 0 fundamental band in a variety of buffer gases using a tunable differencefrequency laser [13][14][15][16][17][18][19][20] or diode laser [21,22]. In addition, microwave data for pure rotational lines [23][24][25][26] as well as Fourier-transform [27][28][29] and diode laser [30] spectra of the overtones have exhibited non-Voigt profiles.…”