Hu Y J, Fu H B, Bernstein E R
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872, USA.
J Chem Phys. 2006 Oct 21;125(15):154306. doi: 10.1063/1.2357953.
We present new observations of the infrared (IR) spectrum of neutral methanol and neutral and protonated methanol clusters employing IR plus vacuum ultraviolet (vuv) spectroscopic techniques. The tunable IR light covers the energy ranges of 2500-4500 cm(-1) and 5000-7500 cm(-1). The CH and OH fundamental stretch modes, the OH overtone mode, and combination bands are identified in the vibrational spectrum of supersonic expansion cooled methanol (2500-7500 cm(-1)). Cluster size selected IR plus vuv nonresonant infrared ion-dip infrared spectra of neutral methanol clusters, (CH(3)OH)(n) (n=2,[ellipsis (horizontal)],8), demonstrate that the methanol dimer has free and bonded OH stretch features, while clusters larger than the dimer display only hydrogen bonded OH stretch features. CH stretch mode spectra do not change with cluster size. These results suggest that all clusters larger than the dimer have a cyclic structure with OH groups involved in hydrogen bonding. CH groups are apparently not part of this cyclic binding network. Studies of protonated methanol cluster ions (CH(3)OH)(n)H(+) n=1,[ellipsis (horizontal)],7 are performed by size selected vuv plus IR photodissociation spectroscopy in the OH and CH stretch regions. Energies of the free and hydrogen bonded OH stretches exhibit blueshifts with increasing n, and these two modes converge to approximately 3670 and 3400 cm(-1) at cluster size n=7, respectively.
我们采用红外加真空紫外（VUV）光谱技术，展示了对中性甲醇以及中性和质子化甲醇团簇的红外（IR）光谱的新观测结果。可调谐红外光覆盖2500 - 4500 cm⁻¹和5000 - 7500 cm⁻¹的能量范围。在超声速膨胀冷却甲醇（2500 - 7500 cm⁻¹）的振动光谱中，识别出了CH和OH基频伸缩模式、OH泛频模式以及组合带。对中性甲醇团簇（CH₃OH）ₙ（n = 2，……，8）进行的团簇尺寸选择红外加VUV非共振红外离子 - 偶极红外光谱表明，甲醇二聚体具有自由和键合的OH伸缩特征，而大于二聚体的团簇仅显示氢键合的OH伸缩特征。CH伸缩模式光谱不随团簇尺寸变化。这些结果表明，所有大于二聚体的团簇都具有环状结构，其中OH基团参与氢键形成。CH基团显然不是这个环状结合网络的一部分。通过在OH和CH伸缩区域进行尺寸选择的VUV加红外光解离光谱，对质子化甲醇团簇离子（CH₃OH）ₙH⁺（n = 1，……，7）进行了研究。自由和氢键合的OH伸缩能量随着n的增加呈现蓝移，并且在团簇尺寸n = 7时，这两种模式分别收敛到约3670和3400 cm⁻¹。
