Pirali O, Kisiel Z, Goubet M, Gruet S, Martin-Drumel M A, Cuisset A, Hindle F, Mouret G
AILES Beamline, Synchrotron SOLEIL, l'Orme des Merisiers, Saint-Aubin, 91192 Gif-sur-Yvette cedex, France.
Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland.
J Chem Phys. 2015 Mar 14;142(10):104310. doi: 10.1063/1.4913750.
Polycyclic aromatic hydrocarbons (PAHs) are highly relevant for astrophysics as possible, though controversial, carriers of the unidentified infrared emission bands that are observed in a number of different astronomical objects. In support of radio-astronomical observations, high resolution laboratory spectroscopy has already provided the rotational spectra in the vibrational ground state of several molecules of this type, although the rotational study of their dense infrared (IR) bands has only recently become possible using a limited number of experimental set-ups. To date, all of the rotationally resolved data have concerned unperturbed spectra. We presently report the results of a high resolution study of the three lowest vibrational states of quinoline C9H7N, an N-bearing naphthalene derivative. While the pure rotational ground state spectrum of quinoline is unperturbed, severe complications appear in the spectra of the ν45 and ν44 vibrational modes (located at about 168 cm(-1) and 178 cm(-1), respectively). In order to study these effects in detail, we employed three different and complementary experimental techniques: Fourier-transform microwave spectroscopy, millimeter-wave spectroscopy, and Fourier-transform far-infrared spectroscopy with a synchrotron radiation source. Due to the high density of states in the IR spectra of molecules as large as PAHs, perturbations in the rotational spectra of excited states should be ubiquitous. Our study identifies for the first time this effect and provides some insights into an appropriate treatment of such perturbations.
多环芳烃（PAHs）与天体物理学高度相关，它们可能是在许多不同天体中观测到的未识别红外发射带的载体，尽管这一点存在争议。为支持射电天文学观测，高分辨率实验室光谱学已经提供了此类几种分子在振动基态下的转动光谱，不过直到最近，利用有限数量的实验装置才得以对其密集红外（IR）带进行转动研究。迄今为止，所有转动分辨数据都涉及未受扰动的光谱。我们目前报告了对喹啉C9H7N（一种含氮萘衍生物）的三个最低振动状态进行高分辨率研究的结果。虽然喹啉的纯转动基态光谱未受扰动，但在ν45和ν44振动模式（分别位于约168厘米⁻¹和178厘米⁻¹处）的光谱中出现了严重的复杂情况。为了详细研究这些效应，我们采用了三种不同且互补的实验技术：傅里叶变换微波光谱学、毫米波光谱学以及使用同步辐射源的傅里叶变换远红外光谱学。由于像PAHs这样的大分子的红外光谱中态密度很高，激发态转动光谱中的扰动应该是普遍存在的。我们的研究首次识别出这种效应，并为适当处理此类扰动提供了一些见解。
