THz spectroscopy and first ISM detection of excited torsional states of¹³C-methyl formate

Abstract

Context. An astronomical survey of interstellar molecular clouds needs a previous analysis of the spectra in the microwave and sub-mm energy range of organic molecules to be able to identify them. We obtained very accurate spectroscopic constants in a comprehensive laboratory analysis of rotational spectra. These constants can be used to predict the transitions frequencies very precisely that were not measured in the laboratory. Aims. We present the experimental study and its theoretical analysis for two 13 C-methyl formate isotopologues to detect these two isotopologues for the first time in their excited torsional states, which lie at 130 cm −1 (200 K) in Orion-KL. Methods. New spectra of HCOO 13 CH 3 ( 13 C 2 ) methyl formate were recorded with the mm-and submm-wave spectrometer in Lille from 50 to 940 GHz. A global fit for v t = 0 and 1 was accomplished with the BELGI program to reproduce the experimental spectra with greater accuracy. Results. We analysed 5728 and 2881 new lines for v t = 0 and 1 for HCOO 13 CH 3 . These new lines were globally fitted with 846 previously published lines for v t = 0. In consequence, 52 parameters of the RAM Hamiltonian were accurately determined and the value of the barrier height (V 3 = 369.93168(395) cm −1 ) was improved. We report the detection of the first excited torsional states (v t = 1) in Orion-KL for the 13 C 2 and 13 C 1 methyl formate based on the present analysis and previously published data. We provide column densities, isotopic abundances, and vibrational temperatures for these species. Conclusions. Following this work, accurate prediction can be provided. This permits detecting 135 features of the first excited torsional states of 13 C-methyl formate isotopologues in Orion-KL in the 80−280 GHz frequency range, without missing lines.

Laboratory characterization and astrophysical detection of vibrationally excited states of vinyl cyanide in Orion-KL

“…Many of these features (near 4000) have been subsequently identified as lines arising from isotopologues, and vibrationally excited states of abundant species, such as ethyl cyanide and methyl formate, thanks to a close collaboration with different spectroscopic laboratories (Demyk et al 2007;Margulès et al 2009;Carvajal et al 2009;Margulès et al 2010;Motiyenko et al 2007;Daly et al 2013;Coudert et al 2013;Haykal et al 2014). In this work, we followed the procedure of our previous papers, searching for all isotopologues and vibrationally excited states of vinyl cyanide in this line survey.…”

13 C-METHYL FORMATE: OBSERVATIONS OF A SAMPLE OF HIGH-MASS STAR-FORMING REGIONS INCLUDING ORION-KL AND SPECTROSCOPIC CHARACTERIZATION

“…In this paper we investigate the carbon isotopic ratio for methyl formate isotopologues and therefore address the issue whether the 12 C/ 13 C ratio is the same for both simple and large molecules. Our analysis is based on recent spectroscopic and laboratory measurements of both the common isotopologue and the 13 C isotopologues (see, Carvajal et al 2007Carvajal et al , 2009Carvajal et al , 2010Ilyushin et al 2009;Kleiner 2010;Margulès et al 2010;Haykal et al 2014, and this study). We would particularly like to stress that in order to derive a 12 C/ 13 C ratio with accuracy and to significantly reduce uncertainties, homogeneous data are a necessity.…”

THz extended spectrum of the monodeuterated methyl formate (DCOOCH3)

“…This formalism and the corresponding software (the BELGICs code) have been applied with success to a number of internal rotor molecules observed in the ISM, such as acetaldehyde CH 3 CHO (Kleiner et al 1996a), acetamide CH 3 CONH 2 (Hollis et al 2006), acetic acid CH 3 COOH (Ilyushin et al 2008(Ilyushin et al , 2013, and different isotopologs of methyl formate (Carvajal et al 2007(Carvajal et al , 2009(Carvajal et al , 2010Ilyushin et al 2009;Margulès et al 2010;Tercero et al 2012;Haykal et al 2014). The BELGI code used in this study is available on the web 1 .…”

“…Since its discovery in Sgr B2 (Brown et al 1975;Churchwell et al 1975), extensive spectroscopic studies have been carried out for the main species (Bauder 1979;Demaison et al 1983;Plummer et al 1984Plummer et al , 1986Oesterling et al 1999;Karakawa et al 2001;Ogata et al 2004;Carvajal et al 2007;Maeda et al 2008b;Ilyushin et al 2009;Full Tudorie et al 2012;Kobayashi et al 2013) and for its isotopologs (Curl 1959;Oesterling et al 1995;Willaert et al 2006;Maeda et al 2008a,b;Margulès et al 2009Margulès et al , 2010Carvajal et al 2009Carvajal et al , 2010Coudert et al 2012Coudert et al , 2013Tercero et al 2012;Haykal et al 2014). This spectroscopic database for the methyl formate molecule has given rise to an increasing identification of the spectral lines in different interstellar surveys.…”

“…In the recent years, a number of molecular line observations toward Orion KL and W51 e2 have been carried out in the ground v t = 0, first v t = 1 and second v t = 2 excited torsional states of main isotopolog (Kobayashi et al 2007;Demyk et al 2008;Favre et al 2011;Takano et al 2012), toward Orion KL, Sgr B2, NGC 6334 IRS 1, W51 e2, and G19.61-023 in the ground and first excited torsional states of the 13 C isotopic substituted species (Carvajal et al 2009;Haykal et al 2014;Favre et al 2014), and toward Orion in the ground state of 18 O species (Tercero et al 2012).…”