Pseudorotational local mode participation in OH and OD(Athinsp;2Sgr;+) vibrational relaxation in a Ne lattice

摘要

Radiationless transitions within theAthinsp;2Sgr;+state of OH and OD in a Ne lattice at 4.2thinsp;deg;K are observed. The radicals are substitutional impurities undergoing slightly perturbed free rotation lsqb;D. S. Tinti, J. Chem. Phys. 48, 1459 (1968)rsqb;. The local phonon relaxation time is quest;10 nsec. Emission spectra show an intermediate strong coupling (or resonant mixing) occurring between rotational levels and lattice phonon levels. Thevprime;=0 lifetimes are 582plusmn;10 and 565plusmn;10 nsec on OH and OD, respectively, with fluorescence quantum yields gsim;0.90. The Lorentzndash;Lorenz dielectric model overestimates the vacuum to solid radiative rate increase by a factor of two. At high radical concentrations Fouml;rster transfer from OD(vprime;=0) to OH(vprime;=0) occurs. The vibrational relaxation rates are fast (4times;104ndash;4times;105secminus;1), with higher rates in OH despite the larger vibrational energy gaps in OH. The rates are extremely sensitive to lattice defects and/or additional impurities causing small (quest;0.3 Aring;) red or blue shifts from the principal site spectra. The principal accepting modes appear to be pseudorotational localized modes. Defects appear to enhance relaxation by creating additional localized modes.