Molecular jet study of aniline–helium van der Waals molecules and aniline radiationless relaxation in the 1B2 excited electronic state

Abstract

Fluorescence excitation (FE), dispersed emission (DE), and time of flight mass spectroscopy (TOFMS) techniques are employed to study the van der Waals molecules formed in a molecular supersonic jet of aniline and helium (AnHe_x). It is found that AnHe₁, AnHe₂, and AnHe₃ have absorption bands that fall under all the An (ν′) vibronic features in the ¹B₂ electronic state of An. The features to the high energy side of the An vibronic transitions are tentatively associated with vibrations of the above van der Waals molecules. The DE from both An and AnHe_x can be characterized as either ‘‘relaxed’’ or ‘‘unrelaxed’’ depending on whether or not the aniline vibronic state emitting is the same as or different from that which was pumped. All ‘‘relaxed’’ An emission can be associated with vibrational predissociation of the AnHe_x species. All ‘‘unrelaxed’’ emission from AnHe_x (ν′+v), with ν′=An mode and v=vdW bond mode, can be associated with Δv=0 transitions from AnHe_x. A number of other relaxation mechanisms are presented and discussed including collisional ones. Some time estimates for the major processes can be discussed.