(HCN)m−Mn (M = K, Ca, Sr): Vibrational Excitation Induced Solvation and Desolvation of Dopants in and on Helium Nanodroplets

详细信息    查看全文

• 作者：Gary E. Douberly ; Paul L. Stiles ; Roger E. Miller ; Roman Schmied ; Kevin K. Lehmann
• 刊名：Journal of Physical Chemistry A
• 出版年：2010
• 出版时间：March 18, 2010
• 年：2010
• 卷：114
• 期：10
• 页码：3391-3402
• 全文大小：432K
• 年卷期：v.114,no.10(March 18, 2010)
• ISSN：1520-5215

文摘

Infrared (IR) laser spectroscopy is used to probe the rotational and vibrational dynamics of the (HCN)_m−M_n (M = K, Ca, Sr) complexes, either solvated within or bound to the surface of helium nanodroplets. The IR spectra of the (HCN)_m−K (m = 1−3), HCN−Sr, and HCN−Ca complexes have the signature of a surface species, similar to the previously reported spectra of HCN−M (M = Na, K, Rb, Cs) [Douberly, G. E.; Miller, R. E. J. Phys. Chem. A 2007, 111, 7292.]. A second band in the HCN−Ca spectrum is assigned to a solvated complex. The relative intesities of the two HCN−Ca bands are droplet size dependent, with the solvated species being favored in larger droplets. IR−IR double resonance spectroscopy is used to probe the interconversion of the two distinct HCN−Ca populations. While only a surface-bound HCN−Sr species is initially produced, CH stretch vibrational excitation results in a population transfer to a solvated state. Complexes containing multiple HCN molecules and one Sr atom are surface-bound, while the ν₁ (HCN)₂Ca spectrum has both the solvated and surface-bound signatures. All HCN−(Ca,Sr)_n (n ≥ 2) complexes are solvated following cluster formation in the droplet. Density-functional calculations of helium nanodroplets interacting with the HCN−M show surface binding for M = Na with a binding energy of 95 cm⁻¹. The calculations predict a fully solvated complex for M = Ca. For M = Sr, a 2.2 cm⁻¹ barrier is predicted between nearly isoenergetic surface binding and solvated states.