Hu Yongjun, Bernstein Elliot R
MOE Key Laboratory of Laser Life Science & Institute of Laser Life Science, South China Normal University, Guangzhou 510631, People's Republic of China.
J Phys Chem A. 2009 Jan 29;113(4):639-43. doi: 10.1021/jp807049e.
Aniline-methanol mixed clusters are ionized by single photon vacuum ultraviolet (VUV, 118 nm) radiation with which absorption to an excited intermediate S(1) state is not required. Aniline ion (An(+)), a series of (An)(n)(+)-(CH(3)OH)(m) (n = 1, 2) cluster ions, and their hydrogenated cluster ions, (An)(n)(+)-(CH(3)OH)(m)H (n = 1, 2) are observed by mass spectrometry. Infrared (IR) absorption spectra of aniline-methanol cluster cations and neutrals are measured through IR and VUV (118 nm) "ion dip" spectroscopy in the range 2500-4000 cm(-1). The observed mid-IR spectrum of the An(+)-CH(3)OH has two sharp absorption bands, at 3438 and 3668 cm(-1), which are assigned to the free NH stretch vibration of the aniline cation and the free OH stretch vibration of methanol, respectively. Calculations demonstrated that a change in the charges on the nitrogen atom of the amine group upon ionization of the neutral to the cluster cation alters the role of aniline from hydrogen acceptor to hydrogen donor in its interaction with methanol. Theoretical and experimental results suggest that a hydrogen bond forms between one of the H atoms of the aniline amine group and the lone pair of electrons of the methanol oxygen atom in the aniline-methanol cluster cation. Measured IR spectra and theoretical results for neutral clusters suggest that the H atom of the methanol OH moiety is bonded to the aniline amine group lone pair electrons for the neutral ground state aniline-methanol cluster.
苯胺 - 甲醇混合团簇通过单光子真空紫外（VUV，118 nm）辐射进行电离，该过程不需要吸收到激发的中间S(1)态。通过质谱观察到苯胺离子（An(+)）、一系列（An）(n)(+)-(CH₃OH)(m)（n = 1, 2）团簇离子及其氢化团簇离子（An）(n)(+)-(CH₃OH)(m)H（n = 1, 2）。通过红外和VUV（118 nm）“离子偶极”光谱在2500 - 4000 cm⁻¹范围内测量了苯胺 - 甲醇团簇阳离子和中性分子的红外（IR）吸收光谱。观察到的An(+) - CH₃OH的中红外光谱有两个尖锐的吸收带，分别位于3438和3668 cm⁻¹，它们分别归属于苯胺阳离子的游离NH伸缩振动和甲醇的游离OH伸缩振动。计算表明，从中性分子电离为团簇阳离子时，胺基氮原子上电荷的变化改变了苯胺在与甲醇相互作用中从氢受体到氢供体的角色。理论和实验结果表明，在苯胺 - 甲醇团簇阳离子中，苯胺胺基的一个H原子与甲醇氧原子的孤对电子之间形成了氢键。中性团簇的测量红外光谱和理论结果表明，对于中性基态苯胺 - 甲醇团簇，甲醇OH部分的H原子与苯胺胺基孤对电子相连。
