Alignment in angular-resolved multiphoton spectra of H 2+

Abstract

Angular resolved kinetic energy distributions of fragments resulting from dissociation induced by intense, short, linearly polarized laser pulses are calculated using an accurate 3D Fourier transform method in spherical coordinates. The rotational excitation of the molecule leads, in general, to an alignment of the photofragments with respect to the field polarization vector. But, unexpectedly, increasing the field strength may also produce less aligned fragments at the higher kinetic energies of the multiphoton above threshold dissociation spectrum. H 2 + photodissociating by interaction with an Nd:YAG laser at (lambda) equals 532 nm and for intensities of 10-50 TW/cm 2 , is taken as an illustrative example, for which some angular resolved experimental spectra are available. A comprehensive interpretation is provided within the field dressed Floquet picture by referring to two strong field mechanisms; namely the potential barrier lowering, and the non-adiabatic transitions. Calculations are presented for three specific initial vibrational states leading to strongly anisotropic angular distributions which are discussed.