Kummli Dominique S, Frey Hans M, Leutwyler Samuel
Departement für Chemie und Biochemie, Universität Bern, Switzerland.
J Chem Phys. 2006 Apr 14;124(14):144307. doi: 10.1063/1.2186642.
Femtosecond degenerate four-wave mixing (fs-DFWM) rotational coherence spectroscopy (RCS) has been used to determine the rotational and centrifugal distortion constants of the 00 (0)0 ground and 01 (1)0 vibrationally excited states of gas-phase CS(2). RCS transients were recorded over the 0-3300 ps optical delay range, allowing the observation of 87 recurrences. The fits yield rotational constants B(00 (0)0)=3.271 549 2(18) GHz for (12)C(32)S(2) and B(00 (0)0)=3.175 06(21) GHz for the (12)C(32)S(34)S isotopomer. The rotational constants of the degenerate 01 (1)0 bending level of (12)C(32)S(2) are B(01 (1)0)=3.276 72(40) and 3.279 03(40) GHz for the e and f substrates, respectively. These fs-DFWM rotational constants are ten times more accurate than those obtained by CO(2) laser/microwave heterodyne measurements and are comparable to those obtained by high-resolution Fourier transform infrared spectroscopy. Ab initio calculations were performed at two levels, second-order Moller-Plesset theory and coupled-cluster singles, doubles, and iterative triples [CCSD(T)]. The equilibrium and vibrationally averaged C=S distances were calculated using large Dunning basis sets. An extrapolation procedure combining the ab initio rotational constants with the experiment yields an equilibrium C=S bond length of 155.448 pm to an accuracy of +/-20 fm. The theoretical C=S bond length obtained by a complete basis set extrapolation at the CCSD(T) level is r(e)(C=S)=155.579 pm, or 0.13 pm longer than that in the experiment.
飞秒简并四波混频（fs-DFWM）旋转相干光谱（RCS）已被用于确定气相CS₂的00(0)0基态和01(1)0振动激发态的转动常数和离心畸变常数。在0至3300皮秒的光学延迟范围内记录了RCS瞬态，从而能够观察到87次重现。拟合得到¹²C³²S₂的转动常数B(00(0)0)=3.2715492(18)吉赫兹，¹²C³²S³⁴S同位素异构体的B(00(0)0)=3.17506(21)吉赫兹。¹²C³²S₂简并的01(1)0弯曲能级的转动常数，对于e和f支，分别为B(01(1)0)=3.27672(40)和3.27903(40)吉赫兹。这些fs-DFWM转动常数比通过CO₂激光/微波外差测量获得的常数精确十倍，并且与通过高分辨率傅里叶变换红外光谱获得的常数相当。在二阶莫勒-普列斯特定理和耦合簇单、双、迭代三激发[CCSD(T)]两个水平上进行了从头算。使用大的邓宁基组计算了平衡和振动平均的C=S距离。将从头算转动常数与实验相结合的外推程序得出平衡C=S键长为155.448皮米，精度为±20飞米。在CCSD(T)水平通过完全基组外推获得的理论C=S键长为r(e)(C=S)=155.579皮米，比实验值长0.13皮米。
