Scaling relations in the rotational excitation of NH(X 3∑−) N=0 by argon

Integral cross sections for rotational transitions out of the lowest rotational level of NH(3∑−)v=0, namely N=0, J=1 F1, induced by collisions with argon have been measured in a crossed beam experiment. A pulsed beam of rotationally cold NH(3∑−) was produced by 193 nm photolysis of a dilute mixture of ammonia in nitrogen seed gas at the tip of a nozzle, the argon beam was also prepared in a pulsed source. The final rotational and spin–state populations were interrogated in the collision zone by laser fluorescence excitation in the A 3Π←X 3∑−(1,0) band of NH. Within a given N′ manifold, the F1 spin level had the largest values for the cross sections out of N=0. The spin–state distributions are, in fact, well described by the general formulas for inelastic collisions of a case (b) 3∑ molecule. The derived spin–free tensor opacities show a rapid decrease as a function of increasing N′.