Rotational alignment of the CN fragment of ICN photodissociation

Abstract

The alignment of the CN fragment following dissociation of ICN has been measured as a function of wavelength by varying the polarization of the tunable laser used for dissociation relative to that of the tunable laser used for laser-induced fluorescence detection of the CN product. The results show that the angular momentum vector of the CN rotor is aligned predominantly perpendicular to the polarization axis of the dissociation laser, in agreement with the expectation for a predominantly parallel absorption in the ICN. However, the degree of alignment is not perfect. The most plausible explanation appears to be that the absorption occurs via a transition that is a mixture of parallel and perpendicular components. Alternate explanations for the imperfect alignment involving either rotation of the ICN parent molecule prior to dissociation or orbital angular momentum during the dissociation are examined and rejected. Near 263–266 nm the transition moment appears to be a mixture of 85% parallel and 15% perpendicular; it becomes more perpendicular to shorter and longer wavelengths.