甲醇团簇的多光子电离质谱及其从头算

用355 nm激光对脉冲分子束超声膨胀冷却的甲醇分子进行多光子电离, 飞行时间质谱仪观测到除甲醇碎片离子外的质子化甲醇团簇(CH3OH)nH+(n=1-16), 且离子的种类及相对强度与激光相对于脉冲分子束的延时无关, 取决于团簇离子内在结构的稳定性. 结合从头算密度泛函理论, 在B3LYP/6-31G(d)基组水平上优化得到了(CH3OH)n和(CH3OH)nH+(n=1-4)的稳定构型. 振动频谱分析显示, 团簇中最强的红外振动模主要来自氢键H伸缩振动的贡献. 团簇电离后发生于团簇内的质子转移反应也可能与激光电离引起的与氢键有关的振动模激发密切相关.

Multiphoton Ionization Mass Spectrum of Methanol Clusters and Ab Initio Calculations

Multiphoton ionization mass spectrum of methanol clusters was studied by using pulsed 355 nm laser to ionize supersonic molecular beam.Besides some fragment ions of methanol,protonated methanol cluster ions(CH3OH)nH (n=1-16)were observed and the cluster's intensity distribution was not affected by laser delay time relative to pulsed molecular beam,which implied that the ions' species and intensity were determined only by cluster's inherent geometric stability.Possible stable geometry structures of(CH3OH)n and(CH3OH)nH (n=1-4)were obtained by using ab initio calculation at B3LYP/6-31G(d)basis level.Comparing cluster's infrared vibrational spectrum with related atomic motion image,it was found that the main contribution to the strongest IR mode came from the H stretch vibration of the hydrogen bond.Proton transfer reaction occurred within clusters after ionization possibly corresponded with the excitation of vibrational mode which is related to hydrogen bond.