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

Abstract

We have recorded the complete infrared spectrum of methane (12)CH4 and its second most abundant isotopomer (13)CH4 extending from the fundamental range starting at 1000 cm(-1) up to the overtone region near 12,000 cm(-1) in the near infrared at the limit towards the visible range, at temperatures of about 80 K and also at 298 K with Doppler limited resolution in the gas phase by means of interferometric Fourier transform spectroscopy using the Bruker IFS 125 HR prototype (ZP 2001) of the ETH Zürich laboratory. This provides the so far most complete data set on methane spectra in this range at high resolution. In the present work we report in particular those results, where the partial rovibrational analysis allows for the direct assignment of pure (J = 0) vibrational levels including high excitation. These results substantially extend the accurate knowledge of vibrational band centers to higher energies and provide a benchmark for both the comparison with theoretical results on the one hand and atmospheric spectroscopy on the other hand. We also present a simple effective Hamiltonian analysis, which is discussed in terms of vibrational level assignments and (13)C isotope effects.

An empirical line list for methane near 1µm (9028–10,435cm−1)

“…A recent contribution by Ulenikov et al [21] is of particular relevance for our work. These authors reported the FTS high resolution spectrum of methane from 1000 to 12,000 cm À 1 at 80 K and 298 K. A multireflection collisional cooling cell with absorption path length between 5 and 15 m was used for the low temperature recordings.…”

“…Unfortunately no line list was constructed and only the P(1) line center values were provided by the authors (Table IV of Ref. [21]). We present in Fig.…”

“…1 illustrates the large gap existing between 9200 and 10,923 cm À 1 which includes the entire tetracontad region (P¼7). To the best of our knowledge, no experimental line list has been published for this polyad yet, while several low resolution spectra available in the literature [11] and recent FTS spectra at 80 K [21] indicate that the tetracontad absorption is relatively strong, similar to that of the neighbor P¼8 polyad. The aim of the present work is then to construct the first empirical line list for the tetracontad by Fourier Transform Spectroscopy at room temperature.…”

“…Rotational cooling in a supersonic jet expansion is the common approach to reduce spectral congestion and simplify rovibrational analysis [2][3][4][5][6][7][8]. Thanks to the significant vapor pressure ($ 10 Torr) available at 80 K, absorption spectra of methane cooled down to liquid nitrogen temperature were recorded in several spectral regions [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Low temperature recordings combined with room temperature data allow applying the so-called "2-Temperaturemethod" which consists of deriving lower state energy level, E emp , of a given transition from the ratio of the intensities of the corresponding line measured at two temperatures [10,15,18].…”

Synchrotron-based highest resolution FTIR spectroscopy of chlorobenzene

“…Further important questions can be addressed by the study of molecules important for the spectroscopy of the Earth's atmosphere [16][17][18][19][20][21][22][23][24]. In the past, much high resolution spectroscopic work has concentrated on relatively simple atmospheric trace gases such as ozone [18], methane [20][21][22][23][24] or some of the simpler fluoro-chloro-hydrocarbons [25], to name just a few selected examples from a very large body of work usually based on FTIR spectroscopy with conventional light sources.…”