Improved centrifugal and hyperfine analysis of ND2H and NH2D and its application to the spectral line survey of L1544

Abstract

Quantifying molecular abundances of astrochemical species is a key step towards the understanding of the chemistry occurring in the interstellar medium. This process requires a profound knowledge of the molecular energy levels, including their structure resulting from weak interactions between nuclear spins and the molecular rotation. With the aim of increasing the quality of spectral line catalogs for the singly-and doubly-deuterated ammonia (NH 2 D and ND 2 H), we have revised their rotational spectra by observing many hyperfine-resolved lines and more accurate high-frequency transitions. The measurements have been performed in the submillimeter-wave region (265-1565 GHz) using a frequency modulation submillimeter spectrometer and in the far-infrared domain (45-220 cm −1 ) with a synchrotron-based Fourier-transform interferometer. The analysis of the new data, with the interpretation of the hyperfine structure supported by state-of-the-art quantum-chemical calculations, led to an overall improvement of all spectroscopic parameters. Moreover, the effect of the inclusion of deuterium splittings in the analysis of astrophysical NH 2 D emissions at millimeter wavelengths has been tested using recent observations of the starless core L1544, an ideal astrophysical laboratory for the study of deuterated species. Our results show that accounting for hyperfine interactions leads to a small but significant change in the physical parameters used to model NH 2 D line emissions.

Protonation of apolar species: From Cl2H+ to (E)-NCCHCHCNH+ through computational investigations

“…Noted is that a nucleus with I > 1/2 has a non-zero quadrupole moment. The hyperfine structure can be useful for the assignment and analysis of rotational lines in the laboratory and in astronomical observations (Turner, 1974;Puzzarini et al, 2010;Melosso et al, 2021); thus, spectral simulations strongly benefit from the introduction of such interaction terms. Both NQCCs and electric dipole moment components were obtained at the ae-CCSD(T)/aug-cc-pwCVQZ level for protonated diatomics, while for CNNCH + the aug-cc-pwCVTZ basis set was used.…”

The Central 1000 au of a Pre-stellar Core Revealed with ALMA. II. Almost Complete Freeze-out

“…We perform the line fit of pNH 2 D(1 11 − 1 01 ) using the nh2d model implemented in pyspeckit (Ginsburg & Mirocha 2011). The pNH 2 D (1 11 -0 01 ) line is modeled using the hyperfine structure and relative intensity from the recent laboratory works of Melosso et al (2020) and Melosso et al (2021). The model assumes a Gaussian velocity distribution (with centroid velocity and velocity dispersion V lsr and σ v ), equal excitation temperatures (T ex ) for all hyperfine components, and total op-tical depth (τ 0 ).…”

“…pH 2 collisional coefficients from Daniel et al (2014) and assumed that the hyperfine components in each rotational level have the same excitation temperature. The hyperfine component frequencies and relative intensities have been adopted from Melosso et al (2021). The velocity profile of the contracting cloud (including a uniform level of turbulence of 0.1 km s −1 ) was taken from Keto et al (2015).…”

Laboratory spectroscopy for astrophysics: Festschrift for Stephan Schlemmer

“…Finally, molecules not belonging to these main categories include an extensive study of the rovibrational spectra of several TiO isotopologs [61], the electronic spectra of C 3 isotopologs with one 13 C [74], a quantum-chemical study of HAlNP [56], an extension of the hyperfine characterization of NH 2 D and NHD 2 [60], the rotational spectroscopy of symmetrically deuterated isotopologs of NH 3 -H 2 [63], and an infrared spectroscopic characterization of SeC 3 Se [75].…”