Rotational spectrum of¹³C₂-methyl formate (HCOO¹³CH₃) and detection of the two¹³C-methyl formate in Orion

Abstract

Context. Laboratory measurements and analysis of the microwave and millimeter-wave spectra of potential interstellar molecules are a prerequisite for their subsequent identification by radioastronomical techniques. The spectral analysis provides spectroscopic parameters that are used in the assignment procedure of the laboratory spectra, and that also predict the frequencies of transitions not measured in the laboratory with a high degree of precision.Aims. An experimental laboratory study and its theoretical analysis is presented for 13 C 2 -methyl formate (HCOO 13 CH 3 ) allowing a search for this isotopologue in the Orion molecular cloud. The 13 C 1 -methyl formate (H 13 COOCH 3 ) molecule was also searched for in this interstellar cloud, using previously published spectroscopic data. Methods. The experimental spectra of 13 C 2 -methyl formate were recorded in the microwave and sub-mm energy ranges (4-20 GHz, 8-80 GHz, 150-700 GHz). The spectra were analyzed using the Rho-Axis Method (RAM), which takes the CH 3 internal rotation and the coupling between internal rotation and global rotation into account. Results. Twenty-seven spectroscopic constants of 13 C 2 -methyl formate have been obtained from a fit of 936 transitions of the ground torsional state with a standard (unitless) deviation of 1.08. A prediction of line positions and intensities is also produced. This prediction allowed us to identify 230 13 C 2 -methyl formate lines in the Orion interstellar molecular cloud. We refitted all previously published ground state transitions of the 13 C 1 -methyl formate molecule in order to provide a prediction of its ground state spectrum. 234 lines of 13 C 1 -methyl formate were detected in the Orion interstellar cloud using that prediction.

TIMASSS: the IRAS 16293-2422 millimeter and submillimeter spectral survey

“…One of the most studied hot cores is the Orion-KL source. Spectral surveys covering almost all the bands accessible from the ground have been obtained, from about 80 to 900 GHz, detecting thousands of lines from hundreds of species and relative isotopologues (see for instance Schilke et al 1997;Lee et al 2001;Comito et al 2005;Olofsson et al 2007;Demyk et al 2007;Carvajal et al 2009;Margulès et al 2009;Tercero et al 2010, and references therein). In addition, the 500-2000 GHz range is observed with the HIFI spectrometer (de Graauw et al 2010) on board the recently launched Herschel 1 satellite (Pilbratt et al 2010), in the Key Program HEXOS 2 .…”

THz extended spectrum of the monodeuterated methyl formate (DCOOCH3)

“…Indeed, in this situation, there is a strong correlation between F and the potential barrier height V 3 (Carvajal et al 2009(Carvajal et al , 2010. For the same reason, the value of the potential parameter V 6 could not be determined.…”

“…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).…”