二羰基茂铁二聚体[CpFe(CO)2]2的中红外泵浦探测光谱

Mid-Infrared Pump-Probe Spectroscopy of Dimeric π-Cyclopentadienyl-dicarbonyliron [CpFe(CO)_2]_2

利用一维稳态红外光谱和5-μm泵浦探测红外光谱手段,结合量子化学计算,以非桥连三价羰基为探针,研究了二羰基茂铁二聚体[CpFe（CO）2]2在二氯甲烷中的结构和振动动力学.结果表明,[CpFe（CO）2]2两个主要结构（顺式cis和反式trans摩尔比为1.7）的振动态寿命和转动动力学都有一定不同.两种结构的两个羰基振动激发态的指数衰减过程都有一个〈1ps的快组分和一个-20ps的慢组分.我们认为前者与宽带激发所产生的振动相干态的快速失相过程有关,而后者属于典型的C≡O伸缩振动态寿命.此外,cis结构与溶剂的较强作用使得其转动衰减较慢.结果表明,非桥连羰基的红外吸收频率和振转动力学对分子结构和溶剂环境都非常敏感.

The structural and vibrational dynamics of the non-bridged C≡O stretching vibrations of two different tautomers of dimeric π-cyclopentadienyldicarbonyliron [CpFe（CO）2]2 in CH2Cl2 were examined using steady-state and femtosecond infrared pump-probe methods at 5-μm wavelength. The two main species in [CpFe（CO）2]2 had a cis：trans molar ratio of 1.7, and showed different vibrational and rotational relaxation dynamics. Both species showed biexponential decay in their two C≡O stretching vibrational excited-state populations, with a fast component （〈1 ps） and a slow component （20 ps）. The former was believed to be related to the rapid dephasing processes of the coherent state caused by broadband excitation, while the latter was the typical lifetime for the C≡O stretching vibrational excited state. Having a significant permanent dipole, the cis structure could interact strongly with solvent, resulting in relatively slower rotational dynamics. Our work demonstrated that the frequency and vibrational-rotational dynamics of the non-bridged C≡O stretching vibrations were very sensitive to both molecular structures and the solvent.