Gianola Adam J, Ichino Takatoshi, Hoenigman Rebecca L, Kato Shuji, Bierbaum Veronica M, Lineberger W Carl
JILA, University of Colorado and National Institute of Standards and Technology, Boulder, Colorado 80309-0440, USA.
J Phys Chem A. 2005 Dec 22;109(50):11504-14. doi: 10.1021/jp053566o.
The 351.1 nm photoelectron spectrum of imidazolide anion has been measured. The electron affinity (EA) of the imidazolyl radical is determined to be 2.613 +/- 0.006 eV. Vibrational frequencies of 955 +/- 15 and 1365 +/- 20 cm(-1) are observed in the spectrum of the (2)B1 ground state of the imidazolyl radical. The main features in the spectrum are well-reproduced by Franck-Condon simulation based on the optimized geometries and the normal modes obtained at the B3LYP/6-311++G(d,p) level of density functional theory. The two vibrational frequencies are assigned to totally symmetric modes with C-C and N-C stretching motions. Overtone peaks of an in-plane nontotally symmetric mode are observed in the spectrum and attributed to Fermi resonance. Also observed is the photoelectron spectrum of the anion formed by deprotonation of imidazole at the C5 position. The EA of the corresponding radical, 5-imidazolyl, is 1.992 +/- 0.010 eV. The gas phase acidity of imidazole has been determined using a flowing afterglow-selected ion tube; delta(acid)G298 = 342.6 +/- 0.4 and delta(acid)H298 = 349.7 +/- 0.5 kcal mol(-1). From the EA of imidazolyl radical and gas phase acidity of imidazole, the bond dissociation energy for the N-H bond in imidazole is determined to be 95.1 +/- 0.5 kcal mol(-1). These thermodynamic parameters for imidazole and imidazolyl radical are compared with those for pyrrole and pyrrolyl radical, and the effects of the additional N atom in the five-membered ring are discussed.
已测量了咪唑阴离子的351.1纳米光电子能谱。确定咪唑基自由基的电子亲和能（EA）为2.613±0.006电子伏特。在咪唑基自由基的（2）B1基态光谱中观察到振动频率为955±15和1365±20厘米⁻¹。基于密度泛函理论B3LYP/6 - 311++G(d,p)水平获得的优化几何结构和简正模式，通过弗兰克 - 康登模拟很好地再现了光谱中的主要特征。这两个振动频率被指定为具有C - C和N - C伸缩运动的完全对称模式。在光谱中观察到面内非完全对称模式的泛音峰，并归因于费米共振。还观察到咪唑在C5位置去质子化形成的阴离子的光电子能谱。相应自由基5 - 咪唑基的EA为1.992±0.010电子伏特。使用流动余辉 - 选择离子管测定了咪唑的气相酸度；δ(acid)G298 = 342.6±0.4和δ(acid)H298 = 349.7±0.5千卡摩尔⁻¹。根据咪唑基自由基的EA和咪唑的气相酸度，确定咪唑中N - H键的键解离能为95.1±0.5千卡摩尔⁻¹。将咪唑和咪唑基自由基的这些热力学参数与吡咯和吡咯基自由基的进行了比较，并讨论了五元环中额外N原子的影响。
