Spectroscopic Evidence for Slow Vibrational and Electronic Relaxation in Solids. The Vegardndash;Kaplan and Second Positive Systems of N2in Solid Rare Gases

摘要

The spectra emitted from N2hyphen;doped rarehyphen;gas solids at low temperatures, irradiated with x rays, have been investigated in detail. The molecular N2emission seen in the spectral range 2300ndash;5000 Aring; consists of the Vegardndash;Kaplan (VK)A3Sgr;uplus;thinsp;rarr;thinsp;X1Sgr;gplus;and the second positiveC3Pgr;uthinsp;rarr;thinsp;B3Pgr;gband systems. The latter is observed only in solid Ne. Forbidden transitions of N atoms and at times of impurity O atoms are also seen. Both N2band systems show emission fromugr;prime;thinsp;thinsp;0, establishing a relatively slow vibrational relaxation rate in theA3Sgr;uplus;andC3Pgr;ustates in solid rare gases. For the VK system the relative intensity of emission fromugr;prime;thinsp;thinsp;0is strongly dependent on the rarehyphen;gas host and on the N2concentration. Nougr;prime;thinsp;thinsp;0is seen for a Ne host, whereas in Ar, Kr, and Xe the relative intensity ofugr;prime;thinsp;thinsp;0increases with decreasing N2concentrations, with a maximum ofugr;prime;thinsp;equals;thinsp;6being found in these three hosts. Decay times for isolated VK bands were measured and appeared exponential within experimental error. From the measured lifetimes it is concluded that the vibrational relaxation time in theA3Sgr;uplus;state of N2in solid rare gases lies between 0.4 and 3.3 sec. The effect of temperature on the relaxation rate was found to be small over the range 1.7deg;ndash;30deg;K. The measured lifetime of theA3Sgr;uplus;state in solid Ne is 3.3 sec, which lies within the range of values reported for the purely radiative lifetime of gaseous N2. A close connection between the processes discussed in this paper and the detailed elementary reactions of radiation chemistry is pointed out.