Photodissociation of jet-cooled NO₂ at 355 nm: Strong alignment and oscillations in the rotational state distributions of the NO(v″=1) fragment

State-to-state photodissociation of NO₂ at 355 nm has been investigated by means of jet-cooling and one-photon laser-induced fluorescence probing techniques. The rotational distribution of nascent NO(??=1) from the fast predissociation of efficiently cooled NO₂ shows pronounced oscillations of each spin-orbit and ?-doublet component and bimodal distributions with preferred population at low and high J. Strong deviations from the statistical distributions of phase space theory are found. Alignment measurements for NO(??=1,J>5.5) from the dissociation of slowly rotating parent molecules are reported for the first time. The well-preserved rotational alignment with a fairly constant value of A₀⁽²⁾ = -(0.35 ± 0.05) confirms that photodissociation at this wavelength is initiated by a ²A₁/²B₂ ? ²A₁ parallel electronic transition with less than 5% contribution from another possible perpendicular transition ²B₁ ? ²A₁. The characteristic rotational distributions observed thus arise from this ²A₁/²B₂ ? ²A₁ transition. Our results clearly show that the energy flow among product rotational degrees of freedom is far from complete and that dynamical effects have to be considered important in the predissociation of NO₂ via the ground-state surface. © 1993 American Chemical Society.