Absolute Fluorescence Yields from Electron Irradiated Gases: XeBr*

Abstract

The techniques of pulse radiolysis and emission spectroscopy have been used to determine absolute total emission yields for the XeBr* exciplex. By application of known formation and quenching rate constants and mechanisms, individual fluorescence yields have been determined for the unquenched three-body ionic recombination reaction, Xe 2 + + Br -+ Xe f XeBr* + 2Xe, G o + ) 3.40 ( 0.18, and for the reaction of electronically excited xenon atoms with CF 3 Br, Xe* + CF 3 Br f XeBr* + CF 3 , G o * ) 0.68 ( 0.10. These experimental yields are compared to the predictions of current theoretical models, which allow calculation of the efficiency for each ion-pair recombination event and excited state reaction to give the fluorescent XeBr* exciplex as 75% and 36%, respectively.

Absolute Fluorescence Yields from Electron-Irradiated Gases. 3. XeCl* and XeI*

“…A sensitivity analysis of the rate constants used in this equation, and their relative errors, shows that this calculated value is only accurate to (25%. This yield is much larger than previously determined for XeBr* (0.68 ( 0.10), 8 KrF* (0.70 ( 0.10), 9 and XeF* (<0.05). 9 From this limiting value, the CFCl 3 pressure dependence of the excited-state fluorescence yield can be calculated, and these values are also shown in Figure 1.…”

“…23 This large rate constant ensured complete formation of Cl -, eliminating any problem with competition from the reaction as seen previously for the Xe/CF 3 Br system. 8 Also, its ionization potential (11.77 eV) 25 is less than that of Xe + (12.130 eV) 26 and thus the charge-transfer reaction will occur in competition with the exciplex formation reactions At high CFCl 3 pressures, the charge-transfer reaction dominates, and thus, the observed exciplex fluorescence is only formed by the energy-transfer pathway. An analysis 27 of the above competition shows that a plot of the inverse of the total yield of XeCl*, G T -1 , against total CFCl 3 pressure will give a limiting straight line at high CFCl 3 pressure, corresponding to the exciplex formation by only the energy-transfer process.…”

“…6 However, the development of powerful gasphase, e-beam-pumped exciplex lasers over the past 20 years has stimulated further investigations in this field, with reported determinations of the total and component process yields in some rare gas systems. 7 In several recent experimental investigations 8,9 absolute fluorescence yields of pulse electron-irradiated rare gas/halogen source gas mixtures (R/AX) for the RX* (B,C) states of XeBr* (Xe/CF 3 Br), 8 KrF* (Kr/SF 6 ), 9 and XeF* (Xe/SF 6 ) 9 have been measured. By modeling of the established [10][11][12][13][14][15][16][17] general mechanism for the formation of these exciplexes, R Df R*, R + , e - RX* f R + X + hν exciplex emission (7) the two formation channels, the energy-transfer (harpooning) reaction of rare gas electronically excited states with the halide gas, reaction 4, and the three-body ionic recombination, reaction 6, have been characterized and their individual fluorescence yields determined for these three species.…”

“…Moreover, despite the KrF* and XeBr* limiting excited-state yields being equal, the ionic recombination value was much larger for XeBr*. 8 This was attributed to the presence of other recombination products, 9 for example, from trimer exciplex formation reactions, being enhanced by the molecular SF 6 -anion being involved in the KrF* recombination.…”

7 Radiation chemistry

“…The ¢rst yield is found to vary from 2.4 (XeCl*) to 0 (XeF*) and the second one from 4.5 (XeI*) to 0.26 (XeF*). 167 The reaction between CF 3 and NO 2 , of special interest for the chemistry of the ozone layer, has been studied by pulse radiolysis combined with time-resolved laser spectroscopy. The rate constants of the two competing reactions gp Q gp Q w 3 g P p T w 1 and gp Q xy P 3 gp P y pxy 2…”