Dependence of impurity zerohyphen;phonon thermal broadening on vibron level in organic crystals: A manifestation of the crystal anharmonicity

摘要

Thermal broadening data on the zerohyphen;phonon impurity bands in the 4500 Aring;1B1larr;1A1and 3500 Aring;1A1larr;1A1absorption systems of 1,3hyphen;diazaazulene and azulene in a naphthalene host are reported. For both systems, a marked dependence of the thermal broadening on the final impurity vibron level of the transition is observed. The broadening for all fundamental vibron bands studied issmallerthan the broadening of the origin or zerohyphen;vibron band. This fact allows one to attribute the above vibron level dependence to a specific anharmonic interaction term (aquarticmixed vibronhyphen;phonon term). It is this term which describes the dependence of the quadratic offhyphen;diagonal electronhyphen;phonon coupling on impurity vibron level. Apparently the vibronhyphen;phonon anharmonic terms which lead to temperature dependent vibron relaxation processes are negligible. We report also the unexpected observation of a dependence of zerohyphen;phonon band thermal broadening on crystal samples. No correlation between this dependence and residual widths is observed.