The fluorescence excitation spectrum of the S1–S0(1B2–1A1) transition in jet-cooled toluene has been measured up to 2000 cm−1 above the origin band. Dispersed fluorescence spectra of the major features have been recorded and used to assign the levels observed in excitation. Collisional energy transfer experiments have been used to confirm assignments for some of the lower lying S1 fundamentals that were not accessible via direct optical pumping. The number of known S1 fundamentals has been extended to 13. The dispersed fluorescence spectra reveal the onset of intramolecular vibrational energy redistribution (IVR) at low S1 vibrational energies. Fluorescence lifetimes of all of the major bands observed in the excitation spectrum have been measured. The lifetimes decrease from 86 ns for 00 to 48 ns at an S1 vibrational energy of 1900 cm−1. To alleviate the confusion that exists over the mode numbering in toluene a new scheme is proposed which obviates this problem. This system is similar to that used for other substituted aromatics and should rationalize future work.
The collision between a Ba atom and an Arn cluster carrying N2O molecules has been investigated under crossed molecular beam conditions. The argon cluster acts as a solvent for the Ba+N2O reaction, which is monitored through its chemiluminescent channel forming electronically excited BaO. The effects of cluster size and the number of N2O molecules per cluster have been investigated systematically as have the effects of extra molecules present upon the cluster (CH4). It has been shown that (i) the BaO reaction product either stays solvated in the cluster or is lost from the cluster; (ii) the reaction probability between Ba and N2O is approximately unity for the clusters considered here; (iii) the chemiluminescence quantum yield decreases as the number of N2O molecules per cluster is increased. The effect of a thermal bath (the argon cluster) on the dynamics of the well studied gas phase reaction Ba+N2O is discussed.
The behaviour of p-nitrophenol (PNP) absorbed at the dodecane/water interface and the interaction with tri-nbutyl phosphate (TBP) were studied by surface second harmonic generation (SHG). The polarisation dependence of the PNP SHG signal, which is the same for all concentrations of PNP and TBP, is best described in terms of a limiting weak orientational order. In the presence of TBP, the SHG signal initially increases with PNP concentration, passes through a maximum and then it decreases. At low PNP concentrations, increasing the TBP concentration leads to an increase in the SHG intensity, but for higher PNP concentrations the intensity decreases. The free energies of adsorption for PNP and TBP to the dodecane/water interface were determined using Frumkin and Langmuir isotherms. The kinetics of the interaction between TBP and PNP was observed by monitoring the SHG signal along a liquidÈliquid Ñow cell and found to be Ðrst-order at high interfacial coverage with rate constant, k, of 0.1 ^0.01 s~1.
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