Rotational state dependence of collision induced line broadening and shift at low temperature

• Published in: The Journal of chemical physics 1999-01, Vol.110 (4), p.2087-2098
• Main Authors: Flatin, Daniel C., Goyette, Thomas M., Beaky, Matthew M., Ball, Christopher D., De Lucia, Frank C.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.477818

The dependence on rotational state of the pressure broadening and shift cross sections of the H2S–H2 and H2S–He systems is reported. The 110–101 and 211–202 transitions of H2S were studied over the temperature range 1–600 K, which includes both the low temperature quantal and the ambient semiclassical collision regimes. At low temperature collisions are mediated by the resonant formation of quasibound complexes rather than the more familiar “action-at-a-distance” mechanisms characteristic of ambient collisions. Additionally, because internal excitation of rotational states can play an important role in the formation of weakly bound complexes, the relation between the rotational energy level spacing hν, and the relative kinetic energy kT plays an important role. The low temperature regime is of interest both because of the interaction mechanism and because it is the regime characteristic of the interstellar medium. Qualitatively, the most interesting features were observed at low temperature, where significantly larger (∼×2) pressure broadening cross sections were measured for the 110–101 than for 211–202.