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Above-threshold dissociation (ATD) process of the molecular ions HD+ steered by a femtosecond laser pulse train (LPT) is investigated theoretically using the time-dependent quantum wave packet method. Energy-dependent distributions of ATD fragments are analyzed by using an asymptotic-flow expression in the momentum space. It is found that fragment kinetic energy spectra shift to low energy region with increasing pulse number of LPT. The photofragment branching ratio between the 1sσg and 2pσu dissociation channels is sensitive to the pulse number of LPT. The momentum distribution of the ATD fragments is discussed in detail.

ABSTRACT:The collision reaction HϩCl ϩ assisted by the ultra-short laser pulse is investigated using the time-dependent quantum wave packet method. The probability of dissociation depends on the yield ratio of association product HCl ϩ . The greater the laser frequency is, the lower the vibrational level of HCl ϩ is. With lowering laser frequency, the probabilities of photoassociation and photodissociation increase, and the ratio of products H ϩ ϩCl( 2 P 0 ) to H( 2 S)ϩCl ϩ ( 1 D) also increases. The kinetic energy spectra of the dissociated fragments at low frequency are wider than those at high frequency.

The multi-photon dissociation of HCl(+) through three channels HCl(+)→H(1s|(2)S)+Cl(+)((3)P), H(+)+Cl((2)P(0)), and H((2)S)+Cl(+)((1)D) steered by intense femtosecond laser pulses are investigated theoretically using the quantum wave packet dynamics. The numerical calculations are performed in two cases without and with the coupling between the excited states. The results show that the dissociation is sensitive to the duration τ, peak intensity I(0), and the resonance of driving laser fields. In the case without the coupling, the effect of the permanent dipole moments on the dissociations dominates for τ < 15 fs, while with the increase of τ, the dissociation dynamics is mainly dominated by the transition dipole moment. In the case with the coupling, the above-threshold dissociation process is complex, and the non-resonant (λ = 400 nm) and resonant (λ = 800 and 1200 nm) laser fields lead to different variation of the branching ratios. The angle-resolved energy distribution is also discussed in detail.