Direct observation of Lambda-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/millim eter-wave double resonance have been used to directly measure the Lambda-do ublet and hyperfine branching ratios and absolute cross-sections of rotatio nally inelastic collisions of NO-He. The data were analyzed in the context of angular momentum recoupling, which is based on the 'spectator' role of t he nuclear spin in the collision, and tensor opacities, which characterize the electrostatic collision. The propensities expected for the approximatel y homonuclear NO (the largest of which is the e/f symmetry conserving, Delt a J = 0 rate) were observed and the four K = 1 tensor opacities measured. ( C) 1999 Elsevier Science B.V. All rights reserved.