Redlich Britta, Zacharias Helmut, Meijer Gerard, von Helden Gert
FOM Institute for Plasma Physics Rijnhuizen, P.O. Box 1207, 3430 BE Nieuwegein, The Netherlands.
J Chem Phys. 2006 Jan 28;124(4):044704. doi: 10.1063/1.2159487.
Resonantly enhanced infrared laser-induced desorption of methane condensed on a single-crystal NaCl(100) surface is observed after excitation with the widely tunable infrared laser output of the free-electron laser at the free-electron laser for infrared experiments facility using mass spectroscopic detection and time-of-flight analysis. Desorption of methane is observed only when the exciting light is in resonance with an internal vibrational mode of the molecule. Different intramolecular modes of the three methane isotopologues under study--CH(4), CD(4), and CD(3)H--are excited; the degenerate deformation mode nu(4) is observed for CH(4) and CD(4) at 7.69 and 10.11 microm, respectively, as well as the nu(2) and nu(4) modes of CD(3)H at 7.79, 9.75, and 9.98 microm. The desorption signals for the pure layers of these different methane isotopologues as well as for different mixtures of two of these are investigated as a function of the infrared wavelength and the laser fluence. The desorption behavior for pure and mixed layers is compared and the underlying desorption mechanism is discussed.
在红外实验用自由电子激光装置中，利用质谱检测和飞行时间分析，通过自由电子激光的宽可调谐红外激光输出进行激发后，观察到了凝聚在单晶NaCl(100)表面的甲烷的共振增强红外激光诱导解吸。仅当激发光与分子的内部振动模式共振时，才观察到甲烷的解吸。研究了三种甲烷同位素分子——CH₄、CD₄和CD₃H——的不同分子内模式被激发的情况；分别在7.69和10.11微米处观察到CH₄和CD₄的简并变形模式ν₄，以及在7.79、9.75和9.98微米处观察到CD₃H的ν₂和ν₄模式。研究了这些不同甲烷同位素分子的纯层以及其中两种的不同混合物的解吸信号随红外波长和激光能量密度的变化情况。比较了纯层和混合层的解吸行为，并讨论了潜在的解吸机制。
