Rotational Dynamics of the Methyl Radical in Superfluid 4He Nanodroplets

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• 作者：Alexander M. Morrison ; Paul L. Raston ; Gary E. Douberly
• 刊名：Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：November 21, 2013
• 年：2013
• 卷：117
• 期：46
• 页码：11640-11647
• 全文大小：396K
• 年卷期：v.117,no.46(November 21, 2013)
• ISSN：1520-5215

文摘

We report the ro-vibrational spectrum of the 谓₃(e鈥? band of the methyl radical (CH₃) solvated in superfluid ⁴He nanodroplets. Five allowed transitions produce population in the N_K = 0₀, 1₁, 1₀, 2₂ and 2₀ rotational levels. The observed transitions exhibit variable Lorentzian line shapes, consistent with state specific homogeneous broadening effects. Population relaxation of the 0₀ and 1₁ levels is only allowed through vibrationally inelastic decay channels, and the ^PP₁(1) and ^RR₀(0) transitions accessing these levels have 4.12(1) and 4.66(1) GHz full-width at half-maximum line widths, respectively. The line widths of the ^PR₁(1) and ^RR₁(1) transitions are comparatively broader (8.6(1) and 57.0(6) GHz, respectively), consistent with rotational relaxation of the 2₀ and 2₂ levels within the vibrationally excited manifold. The nuclear spin symmetry allowed rotational relaxation channel for the excited 1₀ level has an energy difference similar to those associated with the 2₀ and 2₂ levels. However, the ^PQ₁(1) transition that accesses the 1₀ level is 2.3 and 15.1 times narrower than the ^PR₁(1) and ^RR₁(1) lines, respectively. The relative line widths of these transitions are rationalized in terms of the anisotropy in the He-CH₃ potential energy surface, which couples the molecule rotation to the collective modes of the droplet.