Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashiku, Fukuoka 812-8581, Japan.
J Chem Phys. 2010 Oct 21;133(15):154303. doi: 10.1063/1.3478696.
The H(2)C=CD isotopic species of vinyl radical produced in a supersonic jet expansion by ultraviolet laser photolysis was studied by millimeter-wave spectroscopy. Due to the tunneling motion of the α deuteron, the ground state is split into two components, 0(+) and 0(-). Tunneling-rotation transitions connecting the lower (0(+)) and upper (0(-)) components of the tunneling doublet were observed in the frequency region of 184-334 GHz, including three R- and two Q-branch transitions. Three and two pure rotational transitions in the K(a)=0 and 1 stacks, respectively, were also observed for each of the 0(+) and 0(-) states in the frequency region of 52-159 GHz. Least-squares analysis of the observed frequencies for the tunneling-rotation and pure rotational transitions with well resolved hyperfine structures yielded a set of precise molecular constants, among which the tunneling splitting in the ground state was determined to be ΔE(0)=1187.234(17) MHz, which is 1/14 that for H(2)C=CH. The potential barrier height derived from the observed tunneling splitting by an analysis of the tunneling dynamics using a one-dimensional model is 1545 cm(-1), consistent with the value 1568 cm(-1) obtained for the normal vinyl. The observed spectrum was found to be perturbed by a hyperfine interaction connecting ortho and para levels. The constant for the interaction, which we call the ortho-para mixing Fermi contact interaction, has been determined to be δa(F) ((β))=68.06(53) MHz. This is believed to be the first definite detection of such an interaction. By this interaction the ortho and para states of H(2)C=CD are mixed up to about 0.1%. The constant is more than 1000 times larger than spin-rotation interaction constants that cause ortho-para mixing in closed shell molecules and suggests extremely rapid conversion between the ortho and para nuclear spin isomers of H(2)C=CD.
通过紫外激光光解在超音速射流膨胀中产生的乙烯基自由基的 H(2)C=CD 同位素物种，通过毫米波光谱进行了研究。由于α氘的隧道运动，基态分裂成两个分量，0(+)和 0(-)。在 184-334 GHz 的频率区域中，观察到连接隧道双峰的较低（0(+)）和较高（0(-)）分量的隧道-旋转跃迁，包括三个 R-和两个 Q-支跃迁。在 52-159 GHz 的频率区域中，对于 0(+)和 0(-)状态的每个状态，也观察到 K(a)=0 和 1 堆积的三个和两个纯旋转跃迁。对于具有良好分辨的超精细结构的隧道-旋转和纯旋转跃迁的观测频率进行最小二乘法分析，得出了一组精确的分子常数，其中基态的隧道分裂被确定为 ΔE(0)=1187.234(17)MHz，是 H(2)C=CH 的 1/14。通过使用一维模型分析隧道动力学来确定隧道分裂的势垒高度是 1545cm(-1)，与正常乙烯的 1568cm(-1)的值一致。观察到的光谱被超精细相互作用所干扰，该相互作用连接了正和仲能级。相互作用的常数，我们称之为正-仲混合费米接触相互作用，已被确定为 δa(F) ((β))=68.06(53)MHz。这被认为是第一次明确检测到这种相互作用。通过这种相互作用，H(2)C=CD 的正和仲态混合约为 0.1%。该常数比导致闭壳分子正-仲混合的自旋-旋转相互作用常数大 1000 多倍，表明 H(2)C=CD 的正和仲核自旋异构体之间的转换非常迅速。
