Multiphoton dissociative ionization of molecular deuterium

The kinetic energy spectra of deuterium ions produced from D2 arising from collision-free subpicosecond irradiation at 248 nm with intensities spanning the 1013-1016-W/cm2 range have been measured by time-of-flight analysis. The behaviors of the kinetic energy distributions of the fragments and the relative abundances of atomic (D+) and molecular (D2+) ions reveal the presence of two mechanisms of multiphoton dissociative ionization. Calibration of the energy scale for D+ is facilitated by comparison with He2+. For intensities in the 1013-1015-W/cm2 region, intermediate three-photon resonances and the optical Stark shift play important roles. At an intensity 1016 W/cm2, a direct transition from the molecular ground state to the dissociative ionic level appears as a significant channel. No evidence of direct double ionization was observed. © 1988 The American Physical Society.