Hyperfine quantum beats from photolytic orientation and alignment

Abstract

Using Doppler-resolved transient frequency modulation absorption spectroscopy, we have measured both alignment and orientation quantum beats arising from nuclear hyperfine depolarization of low rotational levels of CN X²Σ⁺ photofragments produced in the ultraviolet photodissociation of ICN. Under our conditions of fully resolved fine-structure and completely unresolved hyperfine structure, the observed time evolution is insensitive to the rapid depolarization of angular momentum N that would be observed if the fine-structure components were not resolved. Non-statistical spin-rotation populations of CN photofragments, previously observed only for high rotational states, are now observed even for the lowest rotational states, indicating that the electron can not be considered a spectator spin in the depolarization.