PREPARING REAGENTS - TIME-DEPENDENCE OF HCL(V=1, J) ALIGNMENT FOLLOWING PULSED INFRARED EXCITATION

We discuss the use of photon absorption as a means of aligning reagents for studies of dynamical stereochemistry. A linearly polarized infrared beam from an optical parametric oscillator prepares HCl(nu = 1, J = 1), and the alignment is monitored at subsequent times by (2+1) resonance-enhanced multiphoton ionization. The degree of alignment oscillates in time caused by hyperfine quantum beats. Experimental observations are well matched by calculations that account for the presence of unresolved hyperfine structure. Following reagent preparation by optical pumping, a cumulative hyperfine-depolarization coefficient can be used to describe the effective reagent alignment in a subsequent chemical reaction.