MANIFESTATION OF CHAOTIC NUCLEAR-DYNAMICS OF HIGHLY EXCITED POLYATOMIC-MOLECULES IN TIME-RESOLVED ELECTRON-DIFFRACTION DATA

The effects of chaotic nuclear motion on time-resolved electron diffra ction data recorded of vibrationally highly excited polyatomic molecul es are investigated. For this purpose the time-dependent scattering in tensities are expressed directly in terms of the joint phase space pro bability density in the form of the Wigner function. A simple semiclas sical procedure is described that allows one to obtain the scattering intensities for polyatomic molecules in a state of chaotic nuclear mot ion using internuclear pair potentials. Model calculations show that e lectron diffraction intensities of molecules in a state of chaotic mot ion are clearly different from intensities obtained for systems in a s tate of regular nuclear motion. The procedure was applied to analyze e lectron diffraction data of sulfur hexafluoride, SF6, recorded in the temperature range from 650 K, the spectroscopically determined beginni ng of the quasi-continuum, up to 773 K. The analysis shows that, in th is temperature range, the molecule exists in a state of regular nuclea r motion. This result is remarkable because it indicates that the appe arance of the quasi-continuum does not necessarily indicate the onset of chaotic nuclear motion.