Multiphoton ionisation of H₂and D₂using an intense sub-picosecond laser

The multiphoton ionisation of H 2 and D 2 has been studied using a laser of focused intensity approximately 10 16 W cm -2 , wavelength 600 nm and pulse length 0.6 ps. The H + and D + energy spectra are very similar, with a peak at 3 eV and maximum at about 6 eV. Mass spectra taken with a laser of identical intensity, wavelength 248 nm and pulse length 5 ps have a similar energy spread. The low energies of ions observed here are in sharp contrast to those of the N 2+ and N 3+ ions observed previously in N 2 .