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).
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.
Dallinger
Richard F.
RF
Department of Chemistry, Wabash College, Crawfordsville, Indiana 47933, and Beckman Institute, California Institute of Technology, Pasadena, California 91125.
Carlson
Matt J.
MJ
Miskowski
Vincent M.
VM
Gray
Harry B.
HB