Characteristics and relaxation dynamics of van der Waals complexes between p-difluorobenzene and Ne.

Abstract

Characteristics of the single and double Ne van der Waals complexes of p-difluorobenzene (pDFB) have been explored with ultraviolet fluorescence excitation and dispersed fluorescence spectroscopy. Eight S(1)-S(0) fluorescence excitation bands involving six ring modes of pDFB-Ne and two bands of pDFB-Ne(2) have been identified. Band assignments are confirmed by dispersed fluorescence from the pumped band. Shifts of the complex bands from the analogous monomer bands are generally 4 cm(-1) to the red for pDFB-Ne and 8 cm(-1) for pDFB-Ne(2). None of the observed ring modes is significantly perturbed by complexation in either the S(1) or S(0) states. The pDFB-Ne S(1) van der Waals binding energy D(0')</=120 cm(-1) is inferred from fluorescence band assignments with D(0')-D(0")=4 cm(-1). Vibrational predissociation of pDFB-Ne to produce the S(1) monomer is observed after pumping several levels, but the dissociation process is generally slow compared to fluorescence decay of the complex. Dissociation of the double complex pDFB-Ne(2) occurs from one level to produce S(1) pDFB-Ne in its zero point level. Comparisons are made with the relaxation dynamics of the S(1) complexes pDFB-Ar and pDFB-N(2).