title: Time-Resolved Resonance Raman Spectroscopy at Low Temperature. The Excited-State Metal-Metal Stretching Frequency of Rh(2)(TMB)(4)(2+) (TMB = 2,5-Dimethyl-2,5-diisocyanohexane).
abstract: The time-resolved resonance Raman spectrum of the short-lived triplet (dsigmapsigma) excited state of Rh(2)(TMB)(4)(2+) (TMB = 2,5-dimethyl-2,5-diisocyanohexane) was obtained by lowering the temperature of a 3:1 ethanol/methanol solution until the excited-state lifetime became much greater than the width of the pulsed laser excitation source. The metal-metal stretching frequency is 151 cm(-)(1) in the excited triplet state, as compared to 50 cm(-)(1) in the ground state. The diatomic harmonic force constants derived from these frequencies are in a 9.12:1 ratio (excited state/ground state), consistent with the simple molecular orbital description that predicts that the Rh-Rh bond order is greater in the excited state than in the ground state. A comparison of Rh(2)(TMB)(4)(2+) and Rh(2)b(4)(2+) (b = 1,3-diisocyanopropane) Raman data indicates that the nature of the bridging ligand considerably affects the ground- and excited-state metal-metal stretching frequencies and that the population of the psigma orbital may have very little effect on the bonding in the excited triplet state.
authors.affiliation: Department of Chemistry, Wabash College, Crawfordsville, Indiana 47933, and Beckman Institute, California Institute of Technology, Pasadena, California 91125.
authors.forename: Richard F.
authors.initials: RF
authors.lastname: Dallinger
authors.forename: Matt J.
authors.initials: MJ
authors.lastname: Carlson
authors.forename: Vincent M.
authors.initials: VM
authors.lastname: Miskowski
authors.forename: Harry B.
authors.initials: HB
authors.lastname: Gray