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Using the Yebes 40 m and IRAM 30 m radiotelescopes, we detected two series of harmonically related lines in space that can be fitted to a symmetric rotor. The lines have been seen towards the cold dense cores TMC-1, L483, L1527, and L1544. High level of theory ab initio calculations indicate that the best possible candidate is the acetyl cation, CH3CO+, which is the most stable product resulting from the protonation of ketene. We have produced this species in the laboratory and observed its rotational transitions Ju = 10 up to Ju = 27. Hence, we report the discovery of CH3CO+ in space based on our observations, theoretical calculations, and laboratory experiments. The derived rotational and distortion constants allow us to predict the spectrum of CH3CO+ with high accuracy up to 500 GHz. We derive an abundance ratio N(H2CCO)/N(CH3CO+) ∼ 44. The high abundance of the protonated form of H2CCO is due to the high proton affinity of the neutral species. The other isomer, H2CCOH+, is found to be 178.9 kJ mol−1 above CH3CO+. The observed intensity ratio between the K = 0 and K = 1 lines, ∼2.2, strongly suggests that the A and E symmetry states have suffered interconversion processes due to collisions with H and/or H2, or during their formation through the reaction of H3+ with H2CCO.

The emergence of chemical complexity during star and planet formation is largely guided by the chemistry of unstable molecules that are reaction intermediates in terrestrial chemistry. Our knowledge of these intermediates is limited by both the lack of laboratory studies and the difficulty in their astronomical detection. In this work, we focus on the weakly bound cluster HO3 as an example of the connection between laboratory spectroscopic study and astronomical observations. Here, we present a fast-sweep spectroscopic technique in the millimeter and submillimeter range to facilitate the laboratory search for trans-HO3 and DO3 transitions in a discharge supersonic jet and report their rotational spectra from 70 to 450 GHz. These new measurements enable full determination of the molecular constants of HO3 and DO3. We also present a preliminary search for trans-HO3 in 32 star-forming regions using this new spectroscopic information. HO3 is not detected, and column density upper limits are reported. This work provides additional benchmark information for computational studies of this intriguing radical, as well as a reliable set of molecular constants for extrapolation of the transition frequencies of HO3 for future astronomical observations.

Context. Broadband receivers that operate at millimeter and submillimeter frequencies necessitate the development of new tools for spectral analysis and interpretation. Simultaneous, global, multimolecule, multicomponent analysis is necessary to accurately determine the physical and chemical conditions from line-rich spectra that arise from sources like hot cores. Aims. We aim to provide a robust and efficient automated analysis program to meet the challenges presented with the large spectral datasets produced by radio telescopes. Methods. We have written a program in the MATLAB numerical computing environment for simultaneous global analysis of broadband line surveys. The Global Optimization and Broadband Analysis Software for Interstellar Chemistry (GOBASIC) program uses the simplifying assumption of local thermodynamic equilibrium (LTE) for spectral analysis to determine molecular column density, temperature, and velocity information. Results. GOBASIC achieves simultaneous, multimolecule, multicomponent fitting for broadband spectra. The number of components that can be analyzed at once is only limited by the available computational resources. Analysis of subsequent sets of molecules or components is performed iteratively while taking the previous fits into account. All features of a given molecule across the entire window are fitted at once, which is preferable to the rotation diagram approach because global analysis is less sensitive to blended features and noise features in the spectra. In addition, the fitting method used in GOBASIC is insensitive to the initial conditions chosen, the fitting is automated, and fitting can be performed in a parallel computing environment. These features make GOBASIC a valuable improvement over previously available LTE analysis methods.

A systematic search for carbon-chain cumulenones beyond HCO has been undertaken using microwave spectral taxonomy in combination with a pulsed jet discharge source. No evidence was found for the C isomer of HCO or its longer derivatives, but HC(O)CH, the longer variant of propynal, HC(O)CCH, was identified instead. Its rotational and leading centrifugal distortion constants have been derived to high accuracy from detection of both a- and b-type lines; those below 40 GHz were measured using a Fabry-Perot cavity, while lines between 40 and 72 GHz were recorded by double resonance techniques. Overwhelming evidence for the identification is provided by detection of HC(O)CD, DC(O)CH, and HC(O)CH at the expected frequencies using isotopically enriched samples. Because HC(O)CH is produced with comparable abundance when using either O or CO as the source of oxygen, and because HC(O)CH is not preferentially formed when starting from CO, atomic oxygen appears to be a key reactant in formation, plausibly via O insertion, e.g., HCCH + O → HC(O)CH + H. Under the same experimental conditions, HC(O)CCH is more than 10 times more abundant than HCO, regardless of the source of oxygen, and no evidence is found for cyclopropenone, c-CHO. Taken together, these observations indicate that propynal and longer chains with an odd number of carbon atoms are either energetically more stable than cumulenones of the same size, are kinetically favored products, or both. On the basis of the HC(O)CH discovery, searches for the isovalent sulfur species, HC(S)CH, and HC(O)CH have been conducted. Guided by new quantum chemical calculations, the rotational spectra of both were observed in the centimeter-wave band with the same spectrometer.

Spectral line surveys are an indispensable tool for exploring the physical and chemical evolution of astrophysical environments due to the vast amount of data that can be obtained in a relatively short amount of time. We present deep, broadband spectral line surveys of 30 interstellar clouds using two broadband λ=1.3 mm receivers at the Caltech Submillimeter Observatory. This information can be used to probe the influence of physical environment on molecular complexity. We observed a wide variety of sources to examine the relative abundances of organic molecules as they relate to the physical properties of the source (i.e., temperature, density, dynamics, etc.). The spectra are highly sensitive, with noise levels 25 mK at a velocity resolution of ∼0.35kms −1 . In the initial analysis presented here, column densities and rotational temperatures have been determined for the molecular species that contribute significantly to the spectral line density in this wavelength regime. We present these results and discuss their implications for complex molecule formation in the interstellar medium.

Context. Among the six atoms of N-containing molecules with the formula of CH 3 NO, only formamide (H 2 NCHO), the most stable structural isomer, has been detected in the interstellar medium (ISM). The formaldoxime isomer may be formed, for example, by the reaction of formaldehyde (H 2 CO) or methanimine (H 2 CNH) and hydroxylamine (H 2 NOH), which are all detected in the ISM. The lack of high accuracy millimeter-and submillimeter-wave measurements hinders the astronomical search for formaldoxime. Aims. The aim of this work is to provide the direct laboratory measurement of the millimeter-and submillimeter-wave spectrum of trans-formaldoxime. Methods. Formaldoxime was synthesized and its rotational spectrum was recorded at room temperature in a glass flow cell using the millimeter-and submillimeter-wave spectrometer in Lille. The SPFIT program in the CALPGM suite was used to fit the spectrum. Results. Rotational lines of trans-formaldoxime from both the ground state and v 12 = 1 vibrational excited states have been measured and assigned from 150 to 660 GHz. Spectroscopic constants were derived to the tenth order using both Watson's A and S reduction Hamiltonian.

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