Direct observation of Λ-doublet and hyperfine branching ratios for rotationally inelastic collisions of NO–He at 4.2 K

A 4.2 K collisionally cooling cell and time-resolved millimeter-wave/millimeter-wave double resonance have been used to directly measure the Λ-doublet and hyperfine branching ratios and absolute cross-sections of rotationally inelastic collisions of NO–He. The data were analyzed in the context of angular momentum recoupling, which is based on the `spectatorʹ role of the nuclear spin in the collision, and tensor opacities, which characterize the electrostatic collision. The propensities expected for the approximately homonuclear NO (the largest of which is the e/f symmetry conserving, ΔJ=0 rate) were observed and the four K=1 tensor opacities measured.