arXiv subjects

Adam Walters

Publications and source records attributed to Adam Walters.

3 recordsLinked to original sources

arXiv2019

Rotational spectroscopy, dipole moment and $^{14}$N nuclear hyperfine structure of $iso$-propyl cyanide

Rotational transitions of $iso$-propyl cyanide, (CH$_3$)$_2$CHCN, also known as $iso$-butyronitrile, were recorded using long-path absorption spectroscopy in selected regions between 37 and 600 GHz. Further measurements were carried out between 6 and 20 GHz employing Fourier transform microwave (FTMW) spectroscopy on a pulsed molecular supersonic jet. The observed transitions reach $J$ and $K_a$ quantum numbers of 103 and 59, respectively, and yield accurate rotational constants as well as distortion parameters up to eighth order. The $^{14}$N nuclear hyperfine splitting was resolved in particular by FTMW spectroscopy yielding spin-rotation parameters as well as very accurate quadrupole coupling terms. In addition, Stark effect measurements were carried out in the microwave region to obtain a largely revised $c$-dipole moment component and to improve the $a$-component. The hyperfine coupling and dipole moment values are compared with values for related molecules both from experiment and from quantum chemical calculations.

astro-ph.IM↗

arXiv2016

Laboratory spectroscopic study and astronomical detection of vibrationally excited n-propyl cyanide

We performed a spectral line survey called Exploring Molecular Complexity with ALMA (EMoCA) toward Sagittarius~B2(N) between 84.1 and 114.4 GHz with the Atacama Large Millimeter/submillimeter Array (ALMA) in its Cycles 0 and 1. We determined line intensities of n-propyl cyanide in the ground vibrational states of its gauche and anti conformers toward the hot molecular core Sagittarius B2(N2) which suggest that we should also be able to detect transitions pertaining to excited vibrational states. We wanted to determine spectroscopic parameters of low-lying vibrational states of both conformers of n-propyl cyanide to search for them in our ALMA data. We recorded laboratory rotational spectra of n-propyl cyanide in two spectral windows between 36 and 127 GHz. We searched for emission lines produced by these states in the ALMA spectrum of Sagittarius B2(N2). We modeled their emission and the emission of the ground vibrational states assuming local thermodynamic equilibrium (LTE). We have made extensive assignments of a- and b-type transitions of the four lowest vibrational states of the gauche conformer which reach J and Ka quantum numbers of 65 and 20, respectively. We assigned mostly a-type transitions for the anti conformer with J and Ka quantum numbers up to 48 and 24, respectively. Rotational and Fermi perturbations between two anti states allowed us to determine their energy difference. The resulting spectroscopic parameters enabled us to identify transitions of all four vibrational states of each conformer in our ALMA data. The emission features of all states, including the ground vibrational state, are well-reproduced with the same LTE modeling parameters, which gives us confidence in the reliability of the identifications, even for the states with only one clearly detected line.

astro-ph.GA↗

arXiv2008

Submillimeter Spectrum of Formic Acid

We have measured new submillimeter-wave data around 600 GHz and around 1.1 THz for the 13C isotopologue of formic acid and for the two deuterium isotopomers; in each case for both the trans and cis rotamer. For cis-DCOOH and cis-HCOOD in particular only data up to 50 GHz was previously available. For all species the quality and quantity of molecular parameters has been increased providing new measured frequencies and more precise and reliable frequencies in the range of existing and near-future submillimeter and far-infrared astronomical spectroscopy instruments such as Herschel, SOFIA and ALMA.

astro-ph↗