摘要：

Tunable infrared picosecond pulses in the 5 μ region have been used for time‐resolved pump–probe measurements of the population relaxation lifetime (T1) of CO(v=1) stretching vibrations in a series of metal–carbonyl cluster compounds in room temperature chloroform solution.T1was the same for symmetric (ν=2084 cm1, 90±10 ps) and antisymmetric (2014 cm1, 87±10 ps) modes of the dicarbonyl Rh(CO)2(C5H7O2);T1was the same for theB1(2092 cm1, 710±130 ps) andB2(2036 cm1, 750±90 ps) modes of Rh2(CO)4Cl2. Similarly longT1times were found for Rh4(CO)12(2075 cm1, 610±65 ps) and Rh6(CO)16(2077 cm1, 700±100 ps). The molecule Co4(CO)12has also been compared to the corresponding rhodium analog and it exhibits an initially fast relaxation of 47±5 ps followed by a slower 396±70 ps decay. The transient response of the more complex systems to the single frequency experiment is found to be sensitive to frequency and can exhibit bleaching, absorption, and a combination of these effects. Such behavior is attributed to overlap of the IR pulse withv=1 tov=2 and higher transitions in the M4(CO)12(M=Rh or Co) and Rh6(CO)16molecules. The long CO(v=1)T1values for the metal cluster molecules suggest relaxation via multiquantum transfer of vibrational energy to adjacent M–C stretch and M–C–O bend vibrations; energy transfer to vibrational or electronic states of the central metal core seems unimportant in determiningT1for these systems.

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