Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan.
J Chem Phys. 2012 Dec 21;137(23):234307. doi: 10.1063/1.4770227.
We investigated IR spectra in the CH- and SH-stretching regions of size-selected methanethiol clusters, (CH(3)SH)(n) with n = 2-5, in a pulsed supersonic jet using infrared (IR)-vacuum ultraviolet (VUV) ionization. VUV emission at 132.50 nm served as the source of ionization in a time-of-flight mass spectrometer. Clusters were dissociated with light from a tunable IR laser before ionization. The variations in intensity of methanethiol cluster ions (CH(3)SH)(n)(+) were monitored as the IR laser light was tuned across the range 2470-3100 cm(-1). In the SH-stretching region, the spectrum of (CH(3)SH)(2) shows a weak band near 2601 cm(-1), red-shifted only 7 cm(-1) from that of the monomer. In contrast, all spectra of (CH(3)SH)(n), n = 3-5, show a broad band near 2567 cm(-1) with much greater intensity. In the CH-stretching region, absorption bands of (CH(3)SH)(2) are located near 2865, 2890, 2944, and 3010 cm(-1), red-shifted by 3-5 cm(-1) from those of CH(3)SH. These red shifts increase slightly for larger clusters and bands near 2856, 2884, 2938, and 3005 cm(-1) were observed for (CH(3)SH)(5). These spectral results indicate that the S-H[middle dot][middle dot][middle dot]S hydrogen bond plays an important role in clusters with n = 3-5, but not in (CH(3)SH)(2), in agreement with theoretical predictions. The absence of a band near 2608 cm(-1) that corresponds to absorption of the non-hydrogen-bonded SH moiety and the large width of observed feature near 2567 cm(-1) indicate that the dominant stable structures of (CH(3)SH)(n), n = 3-5, have a cyclic hydrogen-bonded framework.
我们研究了大小选择的甲硫醇团簇（CH(3)SH)(n)，n = 2-5 在 CH 和 SH 伸缩区域的红外光谱，使用红外（IR）-真空紫外（VUV）电离在脉冲超音速射流中。132.50nm 的 VUV 发射用作飞行时间质谱仪中的电离源。在电离之前，用可调谐 IR 激光将团簇解离。当 IR 激光调谐到 2470-3100cm(-1) 范围内时，监测甲硫醇团簇离子（CH(3)SH)(n)(+)的强度变化。在 SH 伸缩区域，（CH(3)SH)(2)的光谱在 2601cm(-1) 附近显示出一个弱带，仅红移 7cm(-1) 从单体。相比之下，（CH(3)SH)(n)，n = 3-5 的所有光谱在 2567cm(-1) 附近显示出一个强度更大的宽带。在 CH 伸缩区域，（CH(3)SH)(2)的吸收带位于 2865、2890、2944 和 3010cm(-1) 附近，从 CH(3)SH 的那些红移 3-5cm(-1)。对于较大的团簇，这些红移略有增加，并且观察到 2856、2884、2938 和 3005cm(-1) 附近的带。这些光谱结果表明，在 n = 3-5 的团簇中，S-H[中间点][中间点][中间点]S 氢键起着重要作用，但在（CH(3)SH)(2)中则没有，这与理论预测一致。不存在对应于非氢键 SH 部分吸收的 2608cm(-1) 附近的带，并且观察到的 2567cm(-1) 附近的特征的大宽度表明（CH(3)SH)(n)，n = 3-5 的主要稳定结构具有环状氢键框架。
