Weichman Marissa L, Kim Jongjin B, Neumark Daniel M
Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Chem Phys. 2014 Mar 14;140(10):104305. doi: 10.1063/1.4867501.
We report high-resolution anion photoelectron spectra of the cryogenically cooled cyanomethide anion, CH2CN(-), and its isotopologue, CD2CN(-), using slow photoelectron velocity-map imaging (SEVI) spectroscopy. Electron affinities of 12 468(2) cm(-1) for CH2CN and 12 402(2) cm(-1) for CD2CN are obtained, demonstrating greater precision than previous experiments. New vibrational structure is resolved for both neutral species, especially activity of the ν5 hydrogen umbrella modes. The ν6 out-of-plane bending mode fundamental frequency is measured for the first time in both systems and found to be 420(10) cm(-1) for CH2CN and 389(8) cm(-1) for CD2CN. Some rotational structure is resolved, allowing for accurate extraction of vibrational frequencies. Temperature-dependent SEVI spectra show marked effects ascribed to controlled population of low-lying anion vibrational levels. We directly measure the inversion splitting between the first two vibrational levels of the anion ν5 umbrella mode in both species, finding a splitting of 130(20) cm(-1) for CH2CN(-) and 81(20) cm(-1) for CD2CN(-). Franck-Condon forbidden activity is observed and attributed to mode-specific vibrational autodetachment from the CH2CN(-) and CD2CN(-) dipole bound excited states. We also refine the binding energy of the anion dipole bound states to 39 and 42 cm(-1), respectively, for CH2CN(-) and CD2CN(-).
我们报道了使用慢光电子速度成像（SEVI）光谱法对低温冷却的氰甲基阴离子CH₂CN⁻及其同位素变体CD₂CN⁻进行的高分辨率阴离子光电子能谱。获得了CH₂CN的电子亲和能为12468(2) cm⁻¹，CD₂CN的电子亲和能为12402(2) cm⁻¹，这表明比之前的实验具有更高的精度。两种中性物种的新振动结构都得到了解析，特别是ν₅氢伞式模式的活性。首次在两个体系中测量了ν₆面外弯曲模式的基频，发现CH₂CN为420(10) cm⁻¹，CD₂CN为389(8) cm⁻¹。解析出了一些转动结构，从而能够准确提取振动频率。温度依赖的SEVI光谱显示出明显的效应，这归因于阴离子低振动能级的可控布居。我们直接测量了两种物种中阴离子ν₅伞式模式前两个振动能级之间的反转分裂，发现CH₂CN⁻的分裂为130(20) cm⁻¹，CD₂CN⁻的分裂为81(20) cm⁻¹。观察到了弗兰克 - 康登禁戒活性，并将其归因于CH₂CN⁻和CD₂CN⁻偶极束缚激发态的模式特异性振动自脱附。我们还将CH₂CN⁻和CD₂CN⁻的阴离子偶极束缚态的结合能分别细化到39和42 cm⁻¹。
