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

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 $S1–S0$ fluorescence excitation bands involving six ring modes of pDFB–Ne and two bands of $pDFB–Ne2$ 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 $pDFB–Ne2.$ None of the observed ring modes is significantly perturbed by complexation in either the $S1$ or $S0$ states. The pDFB–Ne $S1$ van der Waals binding energy $D0′⩽120 cm−1$ is inferred from fluorescence band assignments with $D0′−D0″=4 cm−1.$ Vibrational predissociation of pDFB–Ne to produce the $S1$ 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 $pDFB–Ne2$ occurs from one level to produce $S1$ pDFB–Ne in its zero point level. Comparisons are made with the relaxation dynamics of the $S1$ complexes pDFB–Ar and $pDFB–N2.$