Sando Gerald M, Zhong Q, Owrutsky J C
Code 6111, US Naval Research Laboratory, Washington, DC 20375-5342, USA.
J Chem Phys. 2004 Aug 1;121(5):2158-68. doi: 10.1063/1.1767072.
Ultrafast infrared spectroscopy has been used to measure vibrational energy relaxation (VER) and reorientation (Tr) times for the high frequency vibrational bands of potassium ferrocyanide and ferricyanide (CN stretches), and sodium nitroprusside (SNP, CN, and NO stretches) in water and several other solvents. Relatively short VER times (4-43 ps) are determined for the hexacyano species and for the NO band of SNP, but the CN band of SNP relaxes much more slowly (55-365 ps). The solvent dependence of the VER times is similar for all the solutes and resembles what has been previously observed for triatomic molecular ions [Li et al., J. Chem. Phys. 98, 5499 (1993)]. Anisotropy decay times are also measured from the polarization dependence of the transient absorptions. The Tr times determined for SNP are different for the different vibrational bands; for the nondegenerate NO mode of nitroprusside (SNP) they are much longer (>15 ps), correlate with solvent viscosity, and are attributed to overall molecular rotation. The short Tr (<10 ps) times for the CN band in SNP and for the hexacyanoferrates are due to dipole orientational relaxation in which the transition moment rapidly redistributes among the degenerate modes. There is no evidence of intramolecular vibrational relaxation (IVR) to other high frequency modes. VER times measured for hexacarbonyls and SNP in methanol are similar, which suggests that the generally faster VER for the latter is in part because they are soluble in more strongly interacting polar solvents. The results are compared to those for small ions and metal carbonyls and are discussed in terms of the importance of solute charge and symmetry on VER.
超快红外光谱已被用于测量亚铁氰化钾、铁氰化钾（氰基伸缩振动）以及硝普钠（SNP，氰基和硝基伸缩振动）在水和其他几种溶剂中的高频振动带的振动能量弛豫（VER）和重新取向（Tr）时间。对于六氰基物种和SNP的NO带，确定了相对较短的VER时间（4 - 43皮秒），但SNP的氰基带弛豫要慢得多（55 - 365皮秒）。所有溶质的VER时间对溶剂的依赖性相似，类似于先前对三原子分子离子所观察到的情况[Li等人，《化学物理杂志》98, 5499 (1993)]。还从瞬态吸收的偏振依赖性测量了各向异性衰减时间。SNP不同振动带的Tr时间不同；对于硝普钠（SNP）的非简并NO模式，它们长得多（>15皮秒），与溶剂粘度相关，并归因于整体分子旋转。SNP中氰基带和六氰基铁酸盐的短Tr时间（<10皮秒）是由于偶极取向弛豫，其中跃迁矩在简并模式之间迅速重新分布。没有证据表明存在向其他高频模式的分子内振动弛豫（IVR）。在甲醇中测量的六羰基化合物和SNP的VER时间相似，这表明后者通常较快的VER部分原因是它们可溶于相互作用更强的极性溶剂中。将结果与小离子和金属羰基化合物的结果进行了比较，并根据溶质电荷和对称性对VER的重要性进行了讨论。
