Search

The astrophysical journal 912(2), 90 (2021). doi:10.3847/1538-4357/abe94c, The detection of larger complex organic molecules, such as molecules consisting of several functional groups or those which show conformational flexibility, in the interstellar medium could lead to insights into the availability of biomolecules in space. We present the rotational spectroscopic study of three amino alcohols: alaninol, valinol, and leucinol. The spectra were recorded over the 2–110 GHz region, which included the utilization of a newly developed instrument operating between 18–26 GHz. We report accurately determined line lists, rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants for two conformers of alaninol, four conformers of valinol, and three conformers of leucinol, as well as for several singly substituted heavy-atom isotopologues, which also provide structural insights. Further, a number of spectra of vibrationally excited states were assigned, and the associated motions were revealed with anharmonic frequency calculations. Accurate predictions of rotational transitions into the millimeter-wave regime for all species were made, facilitating searches for these complex molecules by observational facilities such as ALMA. Their detection would establish a new family of interstellar molecules., Published by Univ., Chicago, Ill. [u.a.]

Physical chemistry, chemical physics 22(37), 21474 - 21487 (2020). doi:10.1039/D0CP03523H, The tracking of symmetry-breaking events in space is a long-lasting goal of astrochemists, aiming at an understanding of homochiral Earth chemistry. One current effort at this frontier aims at the detection of small chiral molecules in the interstellar medium. For that, high-resolution laboratory spectroscopy data is required, providing blueprints for the search and assignment of these molecules using radioastronomy. Here, we used chirped-pulse Fourier transform microwave and millimeter-wave spectroscopy and frequency modulation absorption spectroscopy to record and assign the rotational spectrum of the chiral aromatic molecule styrene oxide, C6H5C2H3O, a relevant candidate for future radioastronomy searches. Using experimental data from the 2���12, 75���110, 170���220, and 260���330 GHz regions, we performed a global spectral analysis, which was complemented by quantum chemistry calculations. A global fit of the ground state rotational spectrum was obtained, including rotational transitions from all four frequency regions. Primary rotational constants as well as quartic and sextic centrifugal distortion constants were determined. We also investigated vibrationally excited states of styrene oxide, and for the three lowest energy vibrational states, we determined rotational constants including centrifugal distortion corrections up to the sextic order. In addition, spectroscopic parameters for the singly-substituted 13C and 18O isotopologues were retrieved from the spectrum in natural abundance and used to determine the effective ground state structure of styrene oxide in the gas phase. The spectroscopic parameters and line lists of rotational transitions obtained here will assist future astrochemical studies of this class of chiral organic molecules., Published by RSC Publ., Cambridge

We report here further spectroscopic investigation of the astrochemically relevant molecule i-propyl cyanide. We observed and analysed the rotational spectra of the ground state of the molecule and ten vibrationally excited states with energies between 180–500 cm−1. For this, we used a segmented W-band spectrometer (75–110 GHz) and performed the experiments under room temperature conditions. This approach thus provides access to high-resolution, pure rotational data of vibrational modes that occur in the far-infrared fingerprint region, and that can be difficult to access with other techniques. The obtained, extensive data set will support further astronomical searches and identifications, such as in warmer regions of the interstellar space where contributions from vibrationally excited states become increasingly relevant.

Context. Organic ring compounds play a key role in terrestrial biochemistry, and they were also most likely pivotal ingredients in Earth’s prebiotic chemistry. The five-membered ring imidazole, c-C3N2H4, is a substructure of fundamental biological molecules such as the purine nucleobases and the amino acid histidine. An unsuccessful search for imidazole in a sample of cold-core clouds and massive star-forming regions was performed almost 40 years ago. At that time, the spectroscopic knowledge of this species was scarce: the existing laboratory study was limited to the centimetre-wave region, and the precision of the rest frequencies in the millimetre regime was not adequate. Aims. The goal of the present work is to perform a comprehensive investigation of the rotational spectrum of imidazole in its ground vibrational state from the microwave region to the 1 mm wavelength regime. Methods. The rotational spectrum of imidazole was recorded in selected frequency regions from 2 to 295 GHz. These intervals were covered using various broadband spectrometers developed at DESY (Hamburg) and at the University of Virginia. High-level ab initio calculations were performed to obtain reliable estimates of the quartic and sextic centrifugal distortion constants. We used the EMoCA imaging spectral line survey to search for imidazole towards the hot molecular core Sgr B2(N2). Results. About 700 rotational transitions spanning a J interval from 0 to 59 and Kc interval from 0 to 30 were analysed using the Watson S-reduced Hamiltonian. These new data allowed the determination of a much extended set of spectroscopic parameters for imidazole in its vibrational ground state. The improved spectral data allow us to set an upper limit to the column density of imidazole in Sgr B2(N2). Its non-detection implies that it is at least 3400 times less abundant than ethyl cyanide in this source. Conclusions. With the new set of spectroscopic constants, it has been possible to compute reliable rest frequencies at millimetre wavelengths. We suggest a search for imidazole towards TMC-1, where the aromatic molecule benzonitrile was recently detected.

Journal of molecular spectroscopy 378, 111452 (2021). doi:10.1016/j.jms.2021.111452, We report our analysis of the pure rotational spectra of low-lying vibrationally excited states and heavy-atom rare isotopologues of imidazole. To facilitate searches for imidazole in the interstellar medium, we previously described the analysis of the rotational spectrum of the imidazole main isotopologue across the 2–295 GHz range, and we extend this analysis here. Structure optimisation and anharmonic frequency calculations were performed to aid the spectral analysis. Three vibrationally excited states of imidazole were assigned in our room-temperature spectra, with energies up to approximately 670 cm$^{−1}$ above the vibronic ground state. The vibrational states could act as temperature probes in warmer star-forming regions. The $^{13}$C and $^{15}$N heavy-atom isotopologues were assigned, which allowed for the structure of imidazole in the gas phase to be determined. Structural comparisons are drawn between the related heterocyclic molecules hydantoin and imidazolidine. An experimental gas-phase structure of the former is also determined in this work. The potential detection of the isotopologues could help deduce formation pathways towards imidazole and other nitrogen-containing cyclic compounds in interstellar space., Published by Academic Press, Orlando, Fla.

Isoleucinol, a potential precursor to the essential α-amino acid isoleucine, has been studied using microwave spectroscopy from 2–26 GHz. The measurements between 18–26 GHz were performed with a newly developed segmented chirped-pulse Fourier transform microwave spectrometer, which has reduced the cost of the instrument by half compared to a single pulse excitation and direct detection chirped-pulse microwave spectrometer in the same frequency range. The performance of the instrument has been demonstrated and found to be comparable to the previous design. For isoleucinol, the flexibility of the sec-butyl side chain (R = –CH(CH3)CH2CH3) can result in more than 200 different conformers from its five dihedral angles, and experimentally, seven conformers have been assigned. A fit including the hyperfine splitting due to nitrogen nuclear quadrupole coupling for the rotational transitions is reported for all conformers, along with the experimental structures of the three lowest energy conformers. The observed conformers have intramolecular N⋯H–O hydrogen bond interactions, similar to the second energetically favorable conformer of the analogous amino acid, isoleucine. A complete linelist has been provided to facilitate a search for isoleucinol in the interstellar medium.

Journal of molecular spectroscopy 337, 9 - 16 (2017). doi:10.1016/j.jms.2017.02.017, The astrochemically relevant molecule 1,2-propanediol was investigated at room temperature between 75 and 110 GHz with the aims of providing accurate global rotational constants for its numerous conformers and vibrationally excited states. This was performed with our segmented chirped-pulse millimeter-wave spectrometer. In the spectrum, six previously observed conformers were assigned and treated in global fits, and three vibrationally excited states of the molecule were identified and assigned. The provided transition frequencies of the ground states and vibrationally excited states will aid in the astronomical detection of 1,2-propanediol, specifically in the Atacama Large Millimeter/submillimeter Array Band 3 regime as it overlaps with the frequency range of our spectrometer., Published by Academic Press, Orlando, Fla.