H. Rottke et al., H-2 AND D-2 IN INTENSE SUBPICOSECOND LASER-PULSES - PHOTOELECTRON-SPECTROSCOPY AT 1053 AND 527 NM, Physical review. A, 54(3), 1996, pp. 2224-2237
We report multiphoton ionization experiments on H-2 and D-2 molecules
at 1053- and 526.5-nm excitation wavelengths in the intensity range 5x
10(13)-5x10(14) W/cm(2). The intensity dependence of the total ion yie
ld, the dissociation fraction, and the photoelectron spectrum is inves
tigated. At 1053 nm we find a strong isotope effect in the dissociatio
n fraction, whereas at 526.5 nm no such effect is observed. Up to 1x10
(14) W/cm(2) the photoelectron spectrum at 526.5 nm is dominated by re
sonant ionization processes via Rydberg states of the molecules. They
are shifted into resonance at intensities above similar to 10(13) W/cm
(2). The spectra show that the potential energy curves of the resonant
slates must have a shape very similar to the corresponding ionic ones
. They are therefore mainly determined by the dipole coupling between
the ion core orbitals 1s sigma(g) and 2p sigma(u). At 1053 nm two phot
oionization regimes are observed: the multiphoton regime with Keldysh
parameter gamma>1 showing resonance ionization structures, and the tun
nel regime (gamma<1) at high intensity. The isotope effect in the diss
ociation fraction at 1053 nm has no influence on the shape of the corr
esponding photoelectron spectra at this wavelength.