화학공학소재연구정보센터
Journal of Physical Chemistry, Vol.98, No.47, 12260-12269, 1994
Photodissociation of NO2 at 355-nm and 351-nm Investigated by Photofragment Translational Spectroscopy
The photodissociation of jet-cooled NO2 at 355 and 351 nm has been investigated by polarized high-resolution photofragment translational spectroscopy. The translational energy distributions P(E(T)) of the nascent photofragment pairs NO + O were derived from the measured time-of-flight (TOF) distributions. By comparison of P(E(T)) with the available energy, the population of vibrationally excited NO was determined to be P(nu=0) = 62 +/- 3% and P(nu=1) = 38 -/+ 3% at 355 nm and P(nu=0) = 57 +/- 3% and P(nu=1) = 43 -/+ 3% at 351 nm. These findings are consistent with the trend predicted by statistical models of the dissociation process. Nonstatistical decay dynamics are, however, indicated for the rotational degrees of freedom as manifested by bimodal (or multimodal) rotational distributions of NO(nu=0,1). The recoil anisotropy parameter beta as a function of fragment translational energy was obtained from the polarized TOF spectra and was found to depend on the photolysis wavelength and on the vibrational state of the NO product : beta(nu=0) = 1.42 and beta(nu=1) = 1.25 at 355 nm, whereas beta(nu=0) = 1.77 and beta(nu=1) 1.48 at 351 nm. The NO rotational alignment A(0)((2))) measured by the laser-induced fluorescence method is at high J values close to the theoretical (perpendicular-type) limit of -0.4 at both photolysis wavelengths, This result, in conjunction with the values of beta, implies that the photon absorption occurs via the B-2(2) <-- (2)A(1) electronic transition and that the photodissociation takes place essentially without anisotropy loss and hence on a subpicosecond time scale. The observed dependence of beta on the product vibrational state suggests two different decay pathways with quantum mechanical effects playing an important role.