Self and Polar Foreign Gas Line Broadening and Frequency Shifting of CH3F: Effect of the Speed Dependence Observed by Millimeter-Wave Coherent Transients
✍ Scribed by F. Rohart; A. Ellendt; F. Kaghat; H. Mäder
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 231 KB
- Volume
- 185
- Category
- Article
- ISSN
- 0022-2852
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✦ Synopsis
The shape of the (J, K: 2, 1 R 1, 1) millimeter line of CH 3 F in collision with polar buffer molecules has been investigated in the temperature range 140-300 K. The experiments exploit a Stark switching coherent transient technique, namely the optical free precession phenomenon, the Fourier transform of which is the usual steady state absorption lineshape. Using various buffer gases (CH 3 Br, CH 3 F, and NH 3 ), the observed time domain signals provide the first experimental evidence in the millimeter range that line broadenings as well as frequency shiftings depend on the relative speed of collision partners; that is, lineshapes can become narrowed and asymmetric according to the molecular mass ratio and the type of collisional interaction involved. The experimental signals are analyzed with a time domain speeddependent Voigt profile: for the polar buffer molecules considered, it is shown that a simultaneous interpretation of the broadening and narrowing parameters as well as of their temperature dependence can be satisfactorily obtained only with a realistic collision theory; in contrast with atomic buffer gases, velocity changing collisions play a negligible role.