Effect of laser intensity on (3+1)-photon resonant enhanced multiphoton ionization of a H2 molecule via the B' 1Σu state

The effect of laser intensity on the branching ratios for the vibrational distribution of a H⁺₂ ion and the corresponding photoelectron angular distribution for the (3+1)-photon ionization of a H₂ molecule via the B' ¹Σ_u state have been studied. The branching ratios at the electron scattering angle θ=0° and the asymmetry parameters for photoelectron angular distribution have been calculated in the range of 10⁸-10¹²-W/cm² laser intensity. For ionization via different vibrational levels (v_i=0,1,2) of the B' ¹Σ_u state, the laser-intensity dependence of the branching ratios is prominent in the range 10¹⁰-10¹² W/cm², although the peak of the distribution remains always at Δv=0, i.e., v_i=v_I (v_I is the vibrational level of the ion). Our results have been compared with experimental data of Pratt, Dehmer, and Dehmer [J. Chem. Phys. 85, 3379 (1986); 86, 1727 (1987)].