Triatomic Photofragment Spectra. III. NOCl Photodissociation

Abstract

We have obtained the photofragment spectrum of NOCl in the near ultraviolet at 28 810 cm⁻¹ by 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 70% of the energy in excess of that required to break the ON–Cl bond goes into translational energy of the recoiling fragments. Although vibrational excitation of the NO fragment with v=1, 2, or possibly 3 is energetically allowed, and up to $\text{∼1000\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ may be present in electronic excitation of the NO and Cl, the results are closely matched by a simple modified impulsive model which predicts that v=0 and almost all of the internal energy goes into rotational motion of the NO. The experimental angular distribution peaks along E, the electric vector of the polarized light, and is nearly zero in the plane perpendicular to E, indicating that the transition moment lies in the molecular plane, probably close to the N–Cl bond. This means that the predominant transition at 28 810 cm⁻¹ is to a state of A′ 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 most ${\text{∼8 × 10}}^{\text{−14}}\hspace{0.17em}\sec$ .