Tests of the quasiclassical trajectory cross-correlation moment method against accurate quantum dynamics for V–V energy transfer in HF–HF collisions

V–V energy transfer probabilities for breathing–sphere HF–HF collisions are calculated both by a quasiclassical trajectory moment analysis and by converged quantal close coupling calculations. The two methods agree within factors of 1.1–1.5 for transition probabilities greater than or equal to 0.17 and within factors of 1.9–9.5 for transition probabilities in the range 0.04–0.065, but only within factors of 5.1–82 for those in the range 0.0008–0.004 and within factors of 20–150 for those in the range 0.0002–0.0004.