Synchrotron-based highest resolution Fourier transform infrared spectroscopy of naphthalene (C10H8) and indole (C8H7N) and its application to astrophysical problems

Abstract

We report a rotationally resolved analysis of the high resolution FTIR spectrum of naphthalene which can be considered as a prototypical molecule for polycyclic aromatic hydrocarbons (PAHs), and a similar analysis for the prototypical heterocyclic aromatic molecule indole. The spectra have been measured using a resolution of 0.0008 cm(-1) (21 MHz) with the new high resolution FTIR prototype spectrometer of the Molecular Kinetics and Spectroscopy Group at ETH Zürich. The spectrometer is connected to the infrared port available at the Swiss Light Source (SLS) at the Paul-Scherrer-Institute (PSI). Due to the high brightness of the synchrotron radiation in the spectral region of interest, effectively up to 20 times brighter than thermal sources, and the high resolution of the new interferometer, it was possible to record the rotationally resolved infrared spectra of naphthalene and indole at room temperature, and to analyse the ν46 c-type band (ν̃(0) = 782.330949 cm(-1)) of naphthalene as well as the ν35 c-type band (ν̃(0) = 738.483592 cm(-1)) of indole and an a-type band at ν̃(0) = 790.864370 cm(-1) tentatively assigned as the overtone 2ν(40) of indole. The results of the naphthalene band analysis are discussed in relation to the Unidentified Infrared Band (UIB) found in interstellar spectra at 12.8 μm.

High resolution measurements supported by electronic structure calculations of two naphthalene derivatives: [1,5]- and [1,6]-naphthyridine—Estimation of the zero point inertial defect for planar polycyclic aromatic compounds

“…Recent advances in laboratory techniques permitted to provide interesting and new results to resolve the rotational structure of these bands. Albert et al 14 used the synchrotron radiation as an IR continuum source for the high resolution Fourier transform (FT) spectrometer to record the rotationally resolved absorption spectra of naphthalene and indole in the 600-900 cm −1 region. Brumfield et al 15 studied one band of pyrene (a four rings PAH) by cavity ring down spectroscopy associated to a continuous supersonic jet experiment.…”

Survey of the high resolution infrared spectrum of methane (12CH4 and 13CH4): Partial vibrational assignment extended towards 12 000 cm−1

“…71,[85][86][87][88][89] The nominal instrumental resolution, defined by 1/d MOPD (maximum optical path difference) ranged from 0.0027 to 0.01 cm −1 resulting in almost Doppler limited spectra. The Doppler widths at 78 K range from about 0.004 cm −1 at 2800 cm −1 to 0.02 cm −1 at 12 500 cm −1 .…”

Synchrotron-based Fourier transform spectra of the ν23 and ν24 IR b

“…After the pioneering work of Hewett et al [1] using a molecular beam, the advent of synchrotron-based FT spectroscopy permitted to extend the study of rotationnally resolved IR bands of small Polycyclic Aromatic Hydrocarbons (PAHs) such as naphthalene and its derivatives (see e.g. [2,3] and references therein) and diamondoid-like molecules [4,5]. Hexamethylenetetramine (or HMT), C 6 N 4 H 12 , is strongly suspected to be present in several astrophysical objects such as e.g.…”