JILA, National Institute of Standards and Technology, and Department of Chemistry and Biochemistry, University of Colorado at Boulder , Colorado 80309, United States.
J Phys Chem A. 2013 Dec 19;117(50):13255-64. doi: 10.1021/jp403386d. Epub 2013 Jun 14.
Rovibrational spectroscopy of the fundamental OH stretching mode of the trans-HOCO radical has been studied via sub-Doppler high-resolution infrared laser absorption in a discharge slit-jet expansion. The trans-HOCO radical is formed by discharge dissociation of H2O to form OH, which then combines with CO and cools in the Ne expansion to a rotational temperature of 13.0(6) K. Rigorous assignment of both a-type and b-type spectral transitions is made possible by two-line combination differences from microwave studies, with full rovibrational analysis of the spectrum based on a Watson asymmetric top Hamiltonian. Additionally, fine structure splittings of each line due to electron spin are completely resolved, thus permitting all three ε(aa), ε(bb), ε(cc) spin-rotation constants to be experimentally determined in the vibrationally excited state. Furthermore, as both a- and b-type transitions for trans-HOCO are observed for the first time, the ratio of transition dipole moment projections along the a and b principal axes is determined to be μ(a)/μ(b) = 1.78(5), which is in close agreement with density functional quantum theoretical predictions (B3LYP/6-311++g(3df,3pd), μ(a)/μ(b) = 1.85). Finally, we note the energetic possibility in the excited OH stretch state for predissociation dynamics (i.e., trans-HOCO → H + CO2), with the present sub-Doppler line widths providing a rigorous upper limit of >2.7 ns for the predissociation lifetime.
反式-HOCO 自由基的基态 OH 伸缩模式的振转光谱已通过放电狭缝-射流膨胀中的亚多普勒高分辨率红外激光吸收进行了研究。反式-HOCO 自由基通过 H2O 的放电解离形成 OH，然后与 CO 结合并在 Ne 膨胀中冷却至 13.0(6) K 的转动温度。通过微波研究的双线组合差，有可能对 a 型和 b 型光谱跃迁进行严格的分配，并且基于 Watson 非对称顶哈密顿量对光谱进行了完整的振转分析。此外，由于电子自旋，每条线的精细结构分裂都得到了完全解析，从而允许在振动激发态下实验确定所有三个 ε(aa)、ε(bb)、ε(cc)自旋旋转常数。此外，由于首次观察到反式-HOCO 的 a 型和 b 型跃迁，因此确定了沿着 a 和 b 主轴的跃迁偶极矩投影的比例 μ(a)/μ(b) = 1.78(5)，这与密度泛函量子理论预测（B3LYP/6-311++g(3df,3pd)，μ(a)/μ(b) = 1.85）非常吻合。最后，我们注意到在激发态 OH 伸缩态中存在预解离动力学的能量可能性（即反式-HOCO → H + CO2），目前的亚多普勒线宽为预解离寿命提供了严格的上限 >2.7 ns。
