We have obtained the photofragment spectrum of NOCl in the near ultraviolet at 28 810 cmminus;1by crossing a molecular beam of NOCl with brief pulses of polarized laser light and then measuring the distributions of speed and direction of recoil of the photodissociation fragments. Approximately 70percnt; of the energy in excess of that required to break the ONsngbnd;Cl bond goes into translational energy of the recoiling fragments. Although vibrational excitation of the NO fragment withvequals;1, 2, or possibly 3 is energetically allowed, and up tosim;1000thinsp;cmminus;1may be present in electronic excitation of the NO and Cl, the results are closely matched by a simple modified impulsive model which predicts thatvequals;0 and almost all of the internal energy goes into rotational motion of the NO. The experimental angular distribution peaks alongE, the electric vector of the polarized light, and is nearly zero in the plane perpendicular toE, indicating that the transition moment lies in the molecular plane, probably close to the Nsngbnd;Cl bond. This means that the predominant transition at 28 810 cmminus;1is to a state ofAprime;symmetry. The very high angular anisotropy also shows that the average lifetime in the excited state before dissociation is short compared to the rotational period of the molecule, being at mostsim;8 times; 10minus;14thinsp;sec.
展开▼
