154277-90-4Relevant academic research and scientific papers
Picosecond real-time studies of mode-specific vibrational predissociation
Semmes, David H.,Baskin, J. Spencer,Zewail, Ahmed H.
, p. 3359 - 3376 (1990)
The vibrational predissociation of several van der Waals complexes of t-stilbene has been studied by directly measuring, in real time, the fluorescence intensity from the initial reactant state and from the individual product states formed in the dissociation process after exciting single vibrational levels of the complex.With the aid of a kinetic model involving sequential processes, the individual rates for intramolecular vibrational redistribution and vibrational predissociation in the overall dissociation process are resolved and distinguished in several cases.Inthe stilbene-He complex, the dissociation is significantly faster from low energy out-of-plane modes than it is from a higher energy in-plane mode.
State mixing and vibrational predissociation in large molecule van der Waals complexes: trans-stilbene-X complexes where X=He, H2, Ne, and Ar
DeHaan, David O.,Holton, Alicia L.,Zwier, Timothy S.
, p. 3952 - 3966 (2007/10/02)
We report a detailed study of vibrational predissociation and intramolecular-intermolecular state mixing in the first excited singlet state of trans-stilbene van der Waals complexes with helium, hydrogen, neon, and argon.We present evidence that the helium atom in stilbene-He and the H2 molecule in stilbene-H2 possess very low frequency van der Waals bending levels involving delocalization of the complexed species over both phenyl rings.In stilbene-He, the mode-selective, strong coupling of the out-of-plane phenyl ring modes with the pseudotranslation van der Waals modes leads to a dramatic, inhomogeneous broadening of the transitions to several times their breadth in in-plane vibrations.The observed dispersed fluorescence spectra give product state distributions and internal clock lifetime estimates which can only be made consistent with direct lifetime measurements by assuming extensive state mixing of the intramolecular levels with the van der Waals levels in which the states accessed by the laser are actually only about 30percent intramolecular in character.We conclude that in these complexes the processes of intramolecular-intermolecular state mixing (static IVR) and vibrational predissociation are not independent processes but are closely tied to one another.In fact, the vibrational product state distributions observed for the out-of plane phenyl ring levels can best be interpreted as reflecting the percentage van der Waals character in the initially prepared state.In stilbene-H2 the mode selective coupling exhibits itself as a splitting of the out-of plane transitions into a set of 5-6 closely spaced transitions separated by only about 1 cm-1.The sequence of transitions is suggestive of an in-plane potential for HZ motion which is nearly flat across the entire length of the stilbene molecule with a small barrier presented by the ethylenic carbons through which the H2 molecule can tunnel.Dispersed fluorescence spectra from these levels point to a two-tiered coupling scheme with the bound van der Waals levels.In contrast, the out-of plane phenyl transitions in stilbene-Ne and stilbene-Ar possess unusual shifts, but the transitions are narrow once again.In these cases the complexed atom appears to be largely localized over a single phenyl ring.
