Theory of Pressure-Induced Shifts of Infrared Lines

A treatment is presented that accounts to a large extent for the j dependence of pressure-induced shifts due to noble gases of lines in HCl bands. After a brief critical review of the theoretical work done on this subject to date, an improved phase-shift approximation for the intermolecular collision process is worked out with a coordinate system fixed in space during the collision. The main features of the observed phenomena are accounted for using only parameters calculated directly from known molecular properties. A discussion of the limitations of this theory is given. It appears that in order to achieve further improvement, the finite probability of j transitions and the influence of short-range forces should be taken into account.