Molecular beam study of methyl nitrite photodissociation after excitation into the second absorption band at 248 and 193 nm

The photodissociation dynamics of methyl nitrite in the second UV absorption band (B band) has been studied by molecular beam photofragment spectroscopy at 248 and 193 nm. Angular distributions were measured at both wavelengths yielding anisotropy parameters β=1.36±0.10 at 248 nm and β=1.08±0.07 at 193 nm which indicates a predominantly in plane transition. Measurements performed atT _rot<10 K and atT _rot≧70 K show that within the experimental error β is independent of the rotational temperature of the molecular beam implying that the dissociation process is considerably faster than a typical rotational period. The anglex between the electronic transition moment and the dissociation direction is estimated to be 28° at 248 nm and 34° at 193 nm. The difference ofx at these two wavelengths is proposed to be the effect of an admixture of a perpendicular transition at 193 nm. No contribution attributable to the electronically excited methoxy fragment was found in the TOF spectrum after excitation at 193 nm. It is concluded that the production quantum yield for electronically excited methoxy is smaller than 7%.