Development of ionization detected infrared spectroscopy and its application to overtone spectroscopy of molecules and clusters

本文介绍了一种新的红外光谱技术--非共振电离检测红外光谱(NID-IR)。NID-IR是一种利用紫外光激光选择性电离检测振动激发分子的红外-紫外双共振光谱技术。由于具有电离检测功能，NID-IR光谱与传统的直接吸收红外光谱相比具有很高的灵敏度。NID-IR光谱已应用于苯酚、萘酚和笼胺等多种分子的红外光谱研究。在超音速喷射条件下，观察到了这些分子的红外跃迁。实验结果表明，NID-IR光谱具有较高的灵敏度在2400 cm~(-1)到14000 cm~(-1)范围内，成功地观测到了喷射冷却苯酚的红外跃迁。光谱显示了清晰的振动结构，这是由于OH伸缩、CH泛音和各种组合振动的第一到第四量子。测量了OH伸缩模式的振动频率、自谐性和离解能。结果发现，随着振动量子数的增加，OH泛音的带宽逐渐减小。通过与慢弛豫假设的计算带形的比较，得出了如下结论：结果表明，分子内振动再分配(IVR)引起的谱带展宽是决定谱带形状的主要因素，而在分子内振动再分配(IVR)过程中，可能存在着门道态。

A new IR spectroscopy has been developed.This spectroscopy named nonresonant ionization detected IR spectroscopy (shortly, NID-IR) is a kind of IR- UV double resonance spectroscopy which detects a vibrationally excited molecule by selective ionization due to a UV laser.Because of the ionization detection, NID-IR spectroscopy has very high sensitivity in comparison to the traditional IR spectroscopy due to direct absorption.The NID-IR spectroscopy has been applied to various molecules such as phenol, naphthol and caged amine.The IR transition of these molecule has observed in a supersonic jet condition.In special, IR transition of jet cooled phenol has successfully been observed from 2400 cm-1 to 14000 cm-1.The spectrum shows clear vibrational structures due to the first to the forth quantum of the OH stretching, CH overtones and various combination vibrations.The vibrational frequency, auharmonicity, and the dissociation energy of the OH stretching mode has been measured.It is found that the band width of OH overtones has been decreasing with increase in vibrational quantum number.From the comparison to the calculated band shape assuming slow relaxation, it is concluded that the band shape is mainly determined by the broadening due to the intramolecular vibrational redistribution (IVR).The existence of a doorway state in IVR of phenol has been suggested from the deuterium effect on the band shape.