| Abstrakt: |
Emission spectra (in the region 100–200 nm) of the excimers Ar2*, Kr2*, and Xe2* produced in a dc jet discharge with supersonic expansion were used to determine vibrational temperatures of the excimers, and to analyze the process of excimer relaxation from high vibrational levels near dissociation of the A3Σ+u(1u) states to the lowest levels. The observed narrow bandwidths of the second continua yielded population distributions with at least 80% in the v=0 levels at thermal equilibrium, for all three gases, corresponding to vibrational temperatures of 280, 95, and 82 K for Ar2*, Kr2*, and Xe2*, respectively. Changes in relative intensities of the first and second continua with pressure were monitored by optical pumping of atoms in the 1s5 metastable level [precursor of the excimer A3Σ+u(1u) state], and the resulting difference spectra were analyzed in terms of vibrational relaxation to the v∼0 levels. A simple model based on collisional relaxation was developed to calculate the VUV band spectra. Comparisons of the Ar2* spectra with the model showed that vibrational relaxation accounted for the observed difference spectra, up to plenum pressures of ∼7 atm. Departures from this model at higher pressures for Ar2*, and particularly the observed behavior of Kr2* and Xe2* difference spectra, indicated that populations in the lowest vibrational levels were affected by additional processes, and not only by vibrational relaxation of excimers formed by association. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR] |
