Tao Chong, Mukarakate Calvin, Reid Scott A
Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881, USA.
J Chem Phys. 2006 Jun 14;124(22):224314. doi: 10.1063/1.2204916.
We report new fluorescence excitation and single vibronic level emission spectra of the A (1)A(")<-->X (1)A(') system of CHCl. A total of 21 cold bands involving the pure bending levels 2(0) (n) with n=1-7 and combination bands 2(0) (n)3(0) (1)(n=4-7), 2(0) (n)3(0) (2)(n=4-6), 1(0) (1)2(0) (n)(n=5-7), 1(0) (1)2(0) (n)3(0) (1)(n=4-6), and 1(0) (1)2(0) (n)3(0) (2)(n=4) were observed in the 450-750 nm region; around half of these are reported and/or rotationally analyzed here for the first time. Spectra were measured under jet-cooled conditions using a pulsed discharge source, and rotational analysis typically yielded band origins and rotational constants for both isotopomers (CH(35)Cl,CH(37)Cl). The derived A (1)A(") vibrational intervals are combined with results of Chang and Sears to determine the excited state barrier to linearity [V(b)=1920(50) cm(-1)]. The A (1)A(") state C-H stretching frequency is determined here for the first time, in excellent agreement with ab initio predictions. Following our observation of new bands in this system, we obtained the single vibronic level (SVL) emission spectra which probe the vibrational structure of the X (1)A(') state up to approximately 9000 cm(-1) above the vibrationless level. The total number of X (1)A(') levels observed is around three times than that previously reported, and we observe five new a (3)A(") state levels, including all three fundamentals. The results of a Dunham expansion fit of the ground state vibrational term energies, and comparisons with the previous experimental and recent high level ab initio studies, are reported. Our data confirm the previous assignment of the a (3)A(") origin, and our value for T(00)(a-X)=2172(2) cm(-1) is in excellent agreement with theory. By exploiting SVL spectra from excited state levels with K(a) (')=1, we determine the effective rotational constant (A-B) of the triplet origin, also in good agreement with theory. Our results shed new light on the vibrational structure of the X (1)A('), A (1)A("), and a (3)A(") states of CHCl, and, more generally, spin-orbit coupling in the monohalocarbenes.
我们报道了CHCl的A (1)A(")⇄X (1)A(')体系新的荧光激发光谱和单振动能级发射光谱。在450 - 750 nm区域共观测到21条冷带，涉及纯弯曲能级2(0) (n)（n = 1 - 7）以及组合带2(0) (n)3(0) (1)（n = 4 - 7）、2(0) (n)3(0) (2)（n = 4 - 6）、1(0) (1)2(0) (n)（n = 5 - 7）、1(0) (1)2(0) (n)3(0) (1)（n = 4 - 6）和1(0) (1)2(0) (n)3(0) (2)（n = 4）；其中约一半在此首次报道并进行了转动分析。光谱是在脉冲放电源的喷射冷却条件下测量的，转动分析通常得出两种同位素异构体（CH(35)Cl、CH(37)Cl）的带起源和转动常数。将推导得到的A (1)A(")振动间隔与Chang和Sears的结果相结合，以确定激发态的线性化势垒[V(b)=1920(50) cm(-1)]。本文首次确定了A (1)A(")态的C - H伸缩频率，与从头算预测结果高度吻合。在观测到该体系的新谱带后，我们获得了单振动能级（SVL）发射光谱，该光谱探测了X (1)A(')态在高于无振动能级约9000 cm(-1)范围内的振动结构。观测到的X (1)A(')能级总数约为先前报道的三倍，并且我们观测到五个新的a (3)A(")态能级，包括所有三个基频。报道了基态振动项能量的Dunham展开拟合结果，并与先前的实验和近期高水平的从头算研究进行了比较。我们的数据证实了先前对a (3)A(")起源的归属，并且我们得到的T(00)(a - X)=2172(2) cm(-1)与理论结果高度吻合。通过利用K(a) (') = 1的激发态能级的SVL光谱，我们确定了三重态起源处的有效转动常数（A - B），同样与理论结果相符。我们的结果为CHCl的X (1)A(')、A (1)A(")和a (3)A(")态的振动结构，以及更一般地，单卤代卡宾中的自旋 - 轨道耦合提供了新的见解。
