Collisional transfer between rotational levels of OCS

Steady-state four-level microwave double-resonance experiments are described for pure OCS and OCS diluted with CH₃OH, H₂, and He. For pure OCS, interactions of higher order than first-order dipole-dipole dominate the behavior of some four-level systems, and the rates of ΔJ = 2 quadrupole-type collision-induced transitions are found to be greater than one-half of the ΔJ = 1 dipolar rates. For OCSCH₃OH mixtures, the dipolar rates are significantly enhanced with respect to the pure gas, but ΔJ = 2 transitions are still important. For the mixtures of astrophysical interest, OCSH₂ and OCSHe, all four-level systems show ΔJ = 2 collisional preferences. The ΔJ = 2 transition rates are comparable to those of ΔJ = 1 transitions, and there is evidence that ΔJ = 3 transition rates are substantial.