Spectroscopic study and astronomical detection of vibrationally excited N-propyl cyanide

We have obtained ALMA data of Sagittarius (Sgr for short) B2(N) between 84.0 and 114.4~GHz in its Early Science Cycles 0 and 1. We have focused our analyses on the northern, secondary hot molecular core Sgr~B2(N2) because of the smaller line widths. The survey led to the first detection of a branched alkyl compound, \textit{iso}-propyl cyanide, \textit{i}-C$_3$H$_7$CN, in space\footnote{A. Belloche et al., \textit{Science} {\bf 345} (2014) 1584.} besides the $\sim$2.5 times more abundant straight chain isomer \textit{n}-propyl cyanide, a molecule which we had detected in our IRAM 30~m survey.\footnote{A. Belloche et al., \textit{A\&A} {\bf 499} (2009) 215.} We suspected to be able to detect \textit{n}-propyl cyanide in vibrationally excited states in our ALMA data. We have recorded laboratory rotational spectra of this molecule in three large frequency regions and identified several excited vibrational states. The analyses of these spectra have focused on the 36 to 70~GHz and 89 to 127~GHz regions and on the four lowest excited vibrational states of both the lower lying \textit{gauche}- and the slightly higher lying \textit{anti}-conformer for which rotational constants had been published.\footnote{E. Hirota, \textit{J. Chem. Phys.} {\bf 37} (1962) 2918.} We will present results of our laboratory spectroscopic investigations and will report on the detection of these states toward Sgr~B2(N2)

The spectroscopic parameters of sodium cyanide, NaCN (X 1A'), revisited

The study of the rotational spectrum of NaCN (X $^1$A') has recently been extended in frequency and in quantum numbers. Difficulties have been encountered in fitting the transition frequencies within experimental uncertainties. Various trial fits traced the difficulties to the incomplete diagonalization of the Hamiltonian. Employing fewer spectroscopic parameters than before, the transition frequencies could be reproduced within experimental uncertainties on average. Predictions of $a$-type $R$-branch transitions with $K_a \le 7$ up to 570 GHz should be reliable to better than 1 MHz. In addition, modified spectroscopic parameters have been derived for the 13C isotopic species of NaCN.Comment: 5 pages, no figure, J. Mol. Spectrosc., appeared; CDMS links update

Spectroscopic parameters for silacyclopropynylidene, SiC2_2, from extensive astronomical observations toward CW Leo (IRC +10216) with the Herschel satellite

A molecular line survey has been carried out toward the carbon-rich asymptotic giant branch star CW Leo employing the HIFI instrument on board of the Herschel satellite. Numerous features from 480 GHz to beyond 1100 GHz could be assigned unambiguously to the fairly floppy SiC$_2$ molecule. However, predictions from laboratory data exhibited large deviations from the observed frequencies even after some lower frequency data from this survey were incorporated into a fit. Therefore, we present a combined fit of all available laboratory data together with data from radio-astronomical observations.Comment: 7 pages, 1 figure, J. Mol. Spectrosc., appeared; CDMS links corrected (version 2; current version: 3; may be updated later this year

Rotational spectroscopy of isotopic vinyl cyanide, H2_2C=CH−-C≡\equivN, in the laboratory and in space

The rotational spectra of singly substituted $^{13}$C and $^{15}$N isotopic species of vinyl cyanide have been studied in natural abundances between 64 and 351 GHz. In combination with previous results, greatly improved spectroscopic parameters have been obtained which in turn helped to identify transitions of the $^{13}$C species for the first time in space through a molecular line survey of the extremely line-rich interstellar source Sagittarius B2(N) in the 3 mm region with some additional observations at 2 mm. The $^{13}$C species are detected in two compact ($\sim 2.3''$), hot (170 K) cores with a column density of $\sim 3.8 \times 10^{16}$ and $1.1 \times 10^{16}$ cm$^{-2}$, respectively. In the main source, the so-called ``Large Molecule Heimat'', we derive an abundance of $2.9 \times 10^{-9}$ for each $^{13}$C species relative to H$_2$. An isotopic ratio $^{12}$C/$^{13}$C of 21 has been measured. Based on a comparison to the column densities measured for the $^{13}$C species of ethyl cyanide also detected in this survey, it is suggested that the two hot cores of Sgr B2(N) are in different evolutionary stages. Supplementary laboratory data for the main isotopic species recorded between 92 and 342 GHz permitted an improvement of its spectroscopic parameters as well.Comment: 18 pages, including 2 tables, 3 figures; plus one supplementary text file plus one supplementary pdf file; J. Mol. Spectrosc., in press (to appear in the July or August issue of 2008

Ubiquitous Argonium, Arh+, In The Diffuse Interstellar Medium

ArH$^+$ is isoelectronic with HCl. The $J = 1 - 0$ and $2 - 1$ transitions of $^{36}$ArH$^+$ near 617.5 and 1234.6~GHz, respectively, have been identified very recently as emission lines in spectra obtained with \textit{Herschel} toward the Crab Nebula supernova remnant.\footnote{M.~J. Barlow et al., \textit{Science} \textbf{342} (2013) 1343.} On Earth, $^{40}$Ar is by far the most abundant isotope, being almost exclusively formed by the radioactive decay of $^{40}$K. However, $^{36}$Ar is the dominant isotope in the Universe. In the course of unbiased line surveys of the massive and very luminous Galactic Center star-forming regions Sagittarius~B2(M) and (N) with the high-resolution instrument HIFI on board of \textit{Herschel}, we detected the $J = 1 - 0$ transition of $^{36}$ArH$^+$ as a moderately strong absorption line initially associated with an unidentified carrier.\footnote{H.~S.~P. M{\"u}ller et al., Proceedings of the IAU Symposium 297, 2013, ''The Diffuse Interstellar Bands'', Eds. J. Cami \& N. Cox.} In both cases, the absorption feature is unique in its appearance at all velocity components associated with diffuse foreground molecular clouds, together with its conspicuous absence at velocities related to the denser sources themselves. Model calculations are able to reproduce the derived ArH$^+$ column densities and suggest that argonium resides in the largely atomic, diffuse interstellar medium with a molecular fraction of no more than $\sim$10$^{-4}$. The $^{38}$ArH$^+$ isotopolog was also detected. Subsequent observations toward the continuum sources W51, W49, W31C, and G34.3+0.1 resulted in unequivocal detections of $^{36}$ArH$^+$ absorption. Hence, argonium is a good probe of the transition zone between atomic and molecular gas, in particular in combination with OH$^+$ and H$_2$O$^+$, whose abundances peak at a molecular fraction of $\sim$0.1. Moreover, argonium is a good indicator of an enhanced cosmic ray ionization rate. Therefore, it may be prominent toward, e.g., active galactic nuclei (AGNs) in addition to supernova remnants

Rotational spectroscopy of isotopic oxirane, c-C2H4O

International audienceWe studied the rotational spectrum of oxirane in a sample of natural isotopic composition in selected regions between 158 GHz and 1093 GHz. Investigations of the isotopologs with one 13C or one 18O were the primary focus in order to facilitate searches for them in space. We also examined the main isotopic species mainly to look into the performance of Watson's A and S reductions both in an oblate and in a prolate representation. Even though oxirane is a rather asymmetric oblate rotor, the A reduction in the IIIl representation did not yield a satisfactory fit, as was observed frequently earlier for other molecules. The other three combinations yielded satisfactory fits of similar quality among each other; the A reduction in the Ir representation required two parameters less than both S reduction fits

LEVERAGING DOUBLE-RESONANCE SPECTROSCOPY TO UNDERSTAND TRANS-GLYCIALDEHYDE AND 17 OF ITS VIBRATIONALLY EXCITED STATES

International audienc