RESUMO
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.
RESUMO
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 NH-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.
RESUMO
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.
