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In this paper, new experimental results using UV spectroscopy of the small benzene–Arn clusters are presented. We have found evidence for the vibrational predissociation of the S1 state of some of these species on a nanosecond time scale and we propose a new assignment for the UV spectral features of this system. This assignment is consistent with other experimental data and it accounts additionally for the previously reported spectral anomalies, in particular the ionization potential measurements of these species. The two-color R2PI spectra performed can thus be considered as nanosecond pump–probe experiments that allow us to estimate the relaxation rate of the S1state of these clusters. The vibrational relaxation is found to be strongly size and structure dependent: The two isomers [(1/1) and (2/0)] of the n=2 species exhibit different lifetimes differing by at least one order of magnitude. The size dependence of the relaxation process within the one-sided isomer series appears also paradoxical since th...

Time‐gated fluorescence spectra have been obtained in xenon excited by synchrotron radiation around the first resonance line. Evidence of the emission from the left turning point of the Xe2 excited Ou+ (3P1) potential curve is obtained between 2000 and 2100 A for different excitation wavelengths. From our results, we propose an experimental potential curve for the Ou+ state with an equilibrium distance Re of 3.25 A and a well depth De of 5000 cm−1. Franck–Condon factors have been calculated with this curve for the bound–free transitions between different vibrational levels of the Ou+ excited state and the Og+ ground state. They are in excellent agreement with experiment.

Synchrotron radiation excitation and emission spectra with lifetime measurements are reported for the first time in the VUV region for systems consisting of Cl2 molecules trapped in a neon matrix, an argon matrix, and mixed Ar/Ne matrices. In pure neon, the emission spectrum of the D’→A’ ‘‘laser’’ transition at 4.7 eV of the Cl2 molecule is vibrationally well resolved and constitutes an interesting example of UV spectroscopy of a matrix ‘‘isolated’’ molecule. In pure argon or mixed Ar/Ne matrices, new broad emissions at 4.1, 3.8, and 3.5 eV are clearly identified, which result from the specific interaction between Cl*2 and Ar and are attributed to different charge–transfer states of the ArCl+Cl− entity. The Ar concentration dependence and the time‐gated spectra are shown to be especially useful in interpreting the large differences observed between the pure neon and the pure argon matrix case.

The de‐excitation of the 3P2, 3P1, and 1P1 states of argon was studied in pure argon between 10 and 200 torr and in Ar+CO and Ar+H2 mixtures. These states, which were followed by absorption spectroscopy, are populated after excitation of the gas by a short (20 ns) pulse of 500 keV electrons. The three body rate constants k2, which were not considered in previous low pressure studies, were measured for the two resonant states 3P1(k2=1.7×10−32 cm6 s−1) and 1P1 (k2=0.9×10−32 cm6 s−1). For the metastable 3P2, the measured value of k2 (1.6×10−32 cm6 s−1) is in good agreement with those found in the literature. However, our two body rate constant k1 for the 3P2 state is about ten times higher than values obtained previously from low pressure measurements. The rate constants for the quenching by CO and H2 were measured for the metastable state 3P2 (1.85 and 10.5×10−11 cm3 s−1) and for the resonant states 3P1 (4.5 and 20×10−11 cm3 s−1) and 1P1 (8.5 and 33×10−11 cm3 s−1).

The postluminescence of N2(C 3Πu→ B 3Πg) induced by the transfer of energy to nitrogen by 3P2 metastable argon atoms obtained by the pulsed radiolysis of argon‐nitrogen mixtures has been studied spectrophoto‐electrically. The emission decay lifetime τ is controlled by the destruction of metastable argon atoms. The variation of 1/τ as a function of the argon or nitrogen pressure is used to determine the rate constants k1(Ar*+N2)=3± 0.3 × 10−11cm3sec−1 and k2(Ar*+2Ar)=6± 0.4 × 10−33cm6sec−1. The general reaction process is discussed. The results obtained seem to show that the metastables are formed mainly from the dissociative recombination of Ar2+ ions.