Anomalous angular distribution of fragment ions from rare-gas diatomic molecules with intense, femtosecond, near-infrared laser pulses

摘要

Almost isotropic angular distributions are observed for fragment ions from Xe-2 produced with intense femtosecond laser pulses (800 nm, 4x10(14) W/cm(2)). The results observed for Xe-2 present a great contrast to those for I-2 molecules used as reference molecules, which show typical anisotropic angular distributions resulting from enhanced ionization. The kinetic energy spectra of the fragment ions from Xe-2 reveal that the internuclear distance remains near the equilibrium distance for various pulse widths from 45 to 710 fs, indicating that in the rising edge of the pulses, the internuclear distance of Xe-2 (n+) (n=0, 1, 2) does not reach the favorable region for enhanced ionization even though enhancement can potentially work for Xe-2 (n+). The dynamic alignment of neutral Xe-2 during the pulses is also discussed on the basis of numerical simulations.