Dong F, Heinbuch S, Rocca J J, Bernstein E R
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA.
J Chem Phys. 2006 Oct 21;125(15):154317. doi: 10.1063/1.2348878.
van der Waals cluster (SO2)n is investigated by using single photon ionization of a 26.5 eV soft x-ray laser. During the ionization process, neutral clusters suffer a small fragmentation because almost all energy is taken away by the photoelectron and a small part of the photon energy is deposited into the (SO2)n cluster. The distribution of (SO2)n clusters decreases roughly exponentially with increasing cluster size. The photoionization dissociation fraction of I[(SO2)(n-1)SO+] / I[(SO2)n+] decreases with increasing cluster size due to the formation of cluster. The metastable dissociation rate constants of (SO2)n+ are measured in the range of (0.6-1.5) x 10(4) s(-1) for cluster sizes 5< or =n< or =16. Mixed SO2-H2O clusters are studied at different experimental conditions. At the condition of high SO2 concentration (20% SO2 partial pressure), (SO2)n+ cluster ions dominate the mass spectrum, and the unprotonated mixed cluster ions (SO2)nH2O+ (1< or =n< or =5) are observed. At the condition of low SO2 concentration (5% SO2 partial pressure) (H2O)nH+ cluster ions are the dominant signals, and protonated cluster ions (SO2)(H2O)nH+ are observed. The mixed clusters, containing only one SO2 or H2O molecule, SO2(H2O)nH+ and (SO2)nH2O+ are observed, respectively.
利用26.5 eV软X射线激光的单光子电离对范德瓦尔斯团簇(SO2)n进行了研究。在电离过程中，中性团簇会发生少量碎片化，因为几乎所有能量都被光电子带走，只有一小部分光子能量沉积到(SO2)n团簇中。(SO2)n团簇的分布随团簇尺寸的增加大致呈指数下降。由于团簇的形成，I[(SO2)(n - 1)SO+] / I[(SO2)n+]的光电离解离分数随团簇尺寸的增加而降低。对于5≤n≤16的团簇尺寸，测量了(SO2)n+的亚稳解离速率常数，范围为(0.6 - 1.5)×10(4) s(-1)。在不同实验条件下研究了混合的SO2 - H2O团簇。在高SO2浓度(20% SO2分压)条件下，(SO2)n+团簇离子主导质谱，并且观察到未质子化的混合团簇离子(SO2)nH2O+(1≤n≤5)。在低SO2浓度(5% SO2分压)条件下，(H2O)nH+团簇离子是主要信号，并且观察到质子化团簇离子(SO2)(H2O)nH+。分别观察到仅包含一个SO2或H2O分子的混合团簇SO2(H2O)nH+和(SO2)nH2O+。
