Ion Pair Formation in Multiphoton Excitation of NO2 Using Linearly and Circularly Polarized Femtosecond Light Pulses: Kinetic Energy Distribution and Fragment Recoil Anisotropy

Abstract

The NO(2) ion pair photodissociation dynamics leading to NO(+)(X(1)Sigma(+),v) + O(-)((2)P(3/2) or (2)P(1/2)), induced by a 1 kHz femtosecond laser with wavelengths near 400 nm, has been characterized using the coincidence vector correlation method. The ion pair production after four-photon absorption reaches more than 15% of the primary ionization. The kinetic energy release of the fragments demonstrates a significant vibrational excitation of the NO(+)(X(1)Sigma(+),v) molecular fragment. Recoil ion fragment emission is strongly aligned along the polarization axis of linearly polarized light or preferentially emitted in the plane perpendicular to the propagation axis of circularly polarized light. The formalism describing the recoil anisotropy for bound-to-bound n-photon transition inducing prompt axial recoil dissociation of a nonlinear molecule has been developed to interpret the measured anisotropies in terms of excitation pathways via near-resonant intermediate states of specific symmetries. Possible reaction pathways are discussed that are consistent with the data and supported by calculations of potential energy surfaces and transition moments.