Triatomic Photofragment Spectra. II. Angular Distributions from NO2 Photodissociation

The angular distribution of recoil of O atoms from the photodissociation of NO₂ at 28 810 cm⁻¹ is presented and analyzed to obtain information about the lifetime and symmetry of the excited dissociative state. The theoretical effects on photofragment angular distributions of excited state symmetry, lifetime, angular momentum, and angular recoil distribution with respect to internal coordinates are considered. The actual angular distribution measured by photofragment spectroscopy, peaks in the direction of the electric vector of the light, indicating that the predominant upper state is of ²B₂ symmetry. Some absorption leading to states of different symmetry cannot be excluded. An upper limit for the lifetime of the excited NO₂ molecule before dissociation is ${\text{∼ 2 × 10}}^{\text{−13}}\hspace{0.17em}\sec ,$ indicating that break‐up is too rapid to be affected by collisions in the atmosphere where NO₂ photodissociation is an important step in photochemical air pollution.