AN EFFICIENT TIME-DEPENDENT GOLDEN-RULE TREATMENT FOR 3-DIMENSIONAL VIBRATIONAL PREDISSOCIATION OF HEI2

Two-dimensional (2D) and three-dimensional (3D) quantum calculations for vibrational predissociation of HeI2(B) are carried out using an efficient time-dependent quantum wave packet method based on the Golden Rule approximation. The total decay widths from 2D and 3D calculations of HeI2 predissociation and their dependence on initial vibrational states are presented. Our calculations show that the total decay width from the 2D calculations is almost twice as large as from 3D calculations. It appears clear that the popular T-shaped 2D calculation, in which the rotational motion of the diatomic molecule is neglected, systematically underestimates the lifetime of the complex in agreement with earlier results of Beswick. A plausible explanation is given for why the 2D decay width is larger than the 3D decay width based on the argument of an effective centrifugal barrier. The rotational state distributions of I2 from 3D calculations are insensitive to initial vibrational state, which has also been observed in the HeCl2 system.