Search

The high resolution vibrational spectrum of vinyl acetylene (C2H3CCH) has been investigated in the far infrared region from 180 to 360 cm(-1) using the Bruker IFS 120 HR spectrometer at Justus-Liebig-Universitat, GieEen, Germany. The two energetically lowest vibrational fundamentals nu(13) and nu(18) at 214 cm(-1) and 304 cm(-1), respectively, were measured at a resolution of 0.0016 cm(-1). In addition to the fundamental modes, several hot bands originating from either nu(13) or nu(18) were observed and analyzed. The spectroscopic analysis was supported by high-level quantum-chemical coupled-cluster calculations and also made use of the Automated Spectral Line Assignment Procedure, ASAP, outlined earlier (MartinDrumel et al., 2015). In addition to the infrared study, so far unpublished millimeter-wave vibrational satellites that were measured in the course of an earlier study of the pure rotational spectrum of vinyl acetylene in its ground vibrational state (Thorwirth and Lichau, 2003) were added to the data set and are reported here for the first time. (C) 2021 Elsevier Inc. All rights reserved.

Context. The hydroxymethyl radical (CH2OH) is one of two structural isomers, together with the methoxy radical (CH3O), that can be produced by abstraction of a hydrogen atom from methanol (CH3OH). In the interstellar medium (ISM), both CH2OH and CH3O are suspected to be intermediate species in many chemical reactions, including those of formation and destruction of methanol. The determination of the CH3O/CH2OH ratio in the ISM would bring important information concerning the formation processes of these species in the gas and solid phases. Interestingly, only CH3O has been detected in the ISM so far, despite the recent first laboratory measurement of the CH2OH rotation-tunneling spectrum. This lack of detection is possibly due to the non-observation in the laboratory of the most intense rotation-tunneling transitions at low temperatures.Aims. To support further searches for the hydroxymethyl radical in space, we present a thorough spectroscopic study of its rotation-tunneling spectrum, with a particular focus on transitions involving the lowest quantum numbers of the species.Methods. We recorded the rotation-tunneling spectrum of CH2OH at room temperature in the millimeter-wave domain using a frequency multiplication chain spectrometer. A fluorine-induced H-abstraction method from methanol was used to produce the radical.Results. About 180 transitions were observed, including those involving the lowest N and K-a quantum numbers, which are predicted to be intense under cold astrophysical conditions. These transitions were fitted together with available millimeter-wave lines from the literature. A systematic observation of all components of the rotational transitions yields a large improvement of the spectroscopic parameters allowing confident searches of the hydroxymethyl radical in cold to warm environments of the ISM.

Following the recent discovery of T-shaped GeC2, rotational spectra of three larger Ge carbides, linear GeC4, GeC5, and GeC6 have been observed using chirped pulse and cavity Fourier transform microwave spectroscopy and a laser ablation molecule source, guided by new high-level quantum chemical calculations of their molecular structure. Like their isovalent Si-bearing counterparts, Ge carbides with an even number of carbon atoms beyond GeC2 are predicted to possess (1)sigma ground electronic states, while odd-numbered carbon chains are generally (3)sigma; all are predicted to be highly polar. For the three new molecules detected in this work, rotational lines of four of the five naturally occurring Ge isotopic variants have been observed between 6 and 22 GHz. Combining these measurements with ab initio force fields, the Ge-C bond lengths have been determined to high precision: the derived values of 1.776 angstrom for GeC4, 1.818 angstrom for GeC5, and 1.782 angstrom for GeC6 indicate a double bond between these two atoms. Somewhat surprisingly, the spectrum of GeC5 very closely resembles that of a (1)sigma molecule, implying a spin-spin coupling constant lambda in excess of 770 GHz for this radical, a likely consequence of the large spin-orbit constant of atomic Ge (similar to 1000 cm(-1)). A systematic comparison between the production of SiCn and GeCn chains by laser ablation has also been undertaken. The present work suggests that other large metal-bearing molecules may be amenable to detection by similar means.

Thionitrous acid (HSNO), a potential key intermediate in biological signaling pathways, has been proposed to link NO and H[superscript 2]S biochemistries, but its existence and stability in vivo remain controversial. We establish that HSNO is spontaneously formed in high concentration when NO and H[subscript 2]S gases are mixed at room temperature in the presence of metallic surfaces. Our measurements reveal that HSNO is formed by the reaction H[superscript 2]S + N[subscript 2]O[subscript 3] → HSNO + HNO[subscript 2], where N[superscript 2]O[superscript 3] is a product of NO disproportionation. These studies also suggest that further reaction of HSNO with H[subscript 2]S may form HNO and HSSH. The length of the S–N bond has been derived to high precision and is found to be unusually long: 1.84 Å, the longest S–N bond reported to date for an R-SNO compound. The present structural and, particularly, reactivity investigations of this elusive molecule provide a firm foundation to better understand its potential physiological chemistry and propensity to undergo S–N bond cleavage in vivo.

Thionitrous acid (HSNO), a potential key intermediate in biological signaling pathways, has been proposed to link NO and H₂S biochemistries, but its existence and stability in vivo remain controversial. We establish that HSNO is spontaneously formed in high concentration when NO and H₂S gases are mixed at room temperature in the presence of metallic surfaces. Our measurements reveal that HSNO is formed by the reaction H₂S + N₂O₃ → HSNO + HNO₂, where N₂O₃ is a product of NO disproportionation. These studies also suggest that further reaction of HSNO with H₂S may form HNO and HSSH. The length of the S-N bond has been derived to high precision and is found to be unusually long: 1.84 Å, the longest S-N bond reported to date for an R-SNO compound. The present structural and, particularly, reactivity investigations of this elusive molecule provide a firm foundation to better understand its potential physiological chemistry and propensity to undergo S-N bond cleavage in vivo., United States. National Aeronautics and Space Administration (Grant NNX13AE59G)