Heinbuch S, Dong F, Rocca J J, Bernstein E R
Department of Electrical and Computer Engineering, Colorado State University, Fort Collins, Colorado 80523, USA.
J Chem Phys. 2006 Oct 21;125(15):154316. doi: 10.1063/1.2348877.
Pure neutral (CO2)n clusters and mixed (CO2)n(H2O)m clusters are investigated employing time of flight mass spectroscopy and single photon ionization at 26.5 eV. The distribution of pure (CO2)n clusters decreases roughly exponentially with increasing cluster size. During the ionization process, neutral clusters suffer little fragmentation because almost all excess cluster energy above the vertical ionization energy is taken away by the photoelectron and only a small part of the photon energy is deposited into the (CO2)n cluster. Metastable dissociation rate constants of (CO2)n+ are measured in the range of (0.2-1.5) x 10(4) s(-1) for cluster sizes of 5< or =n< or =16. Mixed CO2-H2O clusters are studied under different generation conditions (5% and 20% CO2 partial pressures and high and low expansion pressures). At high CO2 concentration, predominant signals in the mass spectrum are the (CO2)n+ cluster ions. The unprotonated cluster ion series (CO2)nH2O+ and (CO2)n(H2O)2+ are also observed under these conditions. At low CO2 concentration, protonated cluster ions (H2O)nH+ are the dominant signals, and the protonated CO2(H2O)nH+ and unprotonated (H2O)n+ and (CO2)(H2O)n+ cluster ion series are also observed. The mechanisms and dynamics of the formation of these neutral and ionic clusters are discussed.
采用飞行时间质谱法和26.5 eV的单光子电离技术，对纯中性(CO2)n团簇和混合(CO2)n(H2O)m团簇进行了研究。纯(CO2)n团簇的分布随团簇尺寸的增加大致呈指数下降。在电离过程中，中性团簇几乎不发生碎片化，因为垂直电离能以上的几乎所有多余团簇能量都被光电子带走，只有一小部分光子能量沉积到(CO2)n团簇中。对于5≤n≤16的团簇尺寸，测量了(CO2)n+的亚稳解离速率常数，范围为(0.2 - 1.5)×10(4) s(-1)。在不同的生成条件下(5%和20%的CO2分压以及高和低膨胀压力)研究了混合CO2 - H2O团簇。在高CO2浓度下，质谱中的主要信号是(CO2)n+团簇离子。在这些条件下也观察到了未质子化的团簇离子系列(CO2)nH2O+和(CO2)n(H2O)2+。在低CO2浓度下，质子化团簇离子(H2O)nH+是主要信号，还观察到了质子化的CO2(H2O)nH+以及未质子化的(H2O)n+和(CO2)(H2O)n+团簇离子系列。讨论了这些中性和离子团簇形成的机制和动力学。
