Electronic Absorption Spectra of Matrixhyphen;Isolated Uranium Tetrachloride and Uranium Tetrabromide Molecules

摘要

The electronic absorption spectra of UCl4and UBr4molecules isolated in nitrogen matrices cooled to liquidhyphen;helium temperatures have been observed and measured in the range 400ndash;50 000 cmminus;1. The more than 30 narrow absorption bands, found in the 4000ndash;24 000hyphen;cmminus;1region for each of the two molecules, have been assigned to pure electronic transitions from the3H4lpar;Ggr;5rpar;ground state to excited states of thef2configuration. Energyhyphen;level calculations have been performed by simultaneously diagonalizing the electrostatic, the spinndash;orbit coupling, and the (tetrahedral) crystalhyphen;field interactions. The crystalhyphen;field parameters of fourth and sixth degree, designated asA lang;r4rang;andB lang;r6rang;, were found to be minus;thinsp;593 and minus;thinsp;22 cmminus;1for UCl4and minus;thinsp;490 and minus;thinsp;15 cmminus;1for UBr4. These values of the parameters were obtained by a leasthyphen;squares fit of observedhyphen;tohyphen;calculated energy levels allowingA lang;r4rang;andB lang;r6rang;to vary while maintaining the values ofF2, F4, F6, andzgr;5fat 191, 34, 4, and 1796 cmminus;1, respectively. The magnitudes ofA lang;r4rang;andB lang;r6rang;calculated on the basis of a pointhyphen;charge model including induced dipole contributions were found to be minus;thinsp;345 and 26 cmminus;1for UCl4and minus;thinsp;309 and 22 cmminus;1for UBr4.