Laboratory Rotational Spectra of Silyl Isocyanide

TL;DR

This study reports the laboratory detection and spectroscopic analysis of silyl isocyanide (SiH3NC), an isomer of silyl cyanide, providing data crucial for its potential astronomical identification in space environments.

Contribution

The paper provides the first laboratory rotational spectrum of SiH3NC, including spectroscopic constants and hyperfine structure, enabling future astronomical searches for this molecule.

Findings

Spectroscopic constants derived for SiH3NC enable precise astronomical transition predictions.

The abundance ratio of SiH3NC to SiH3CN is about 1:3 in the molecular beam.

SiH3NC is a promising candidate for detection in space due to its similar properties to known molecules.

Abstract

The rotational spectrum of silyl isocyanide (SiH$_3$NC), an isomer of the well studied silyl cyanide (SiH$_3$CN), has been detected in the laboratory in a supersonic molecular beam, and the identification was confirmed by observations of the corresponding rotational transitions in the rare isotopic species SiH$_3$$^{15}$NC and SiH$_3$N$^{13}$C. Spectroscopic constants derived from 19 transitions between $11 - 35$~GHz in the three lowest harmonically related rotational transitions in the $K = 0 ~{\rm{and}}~1$ ladders of the normal isotopic species including the nitrogen nuclear quadrupole hyperfine constant, allow the principal astronomical transitions of SiH$_3$NC to be calculated to an uncertainty of about 4~km~s$^{-1}$ in equivalent radial velocity, or within the FWHM of narrow spectral features in the inner region of IRC+10216 near 200~GHz. The concentration of SiH$_3$NC in our molecular beam is three times less than SiH$_3$CN, or about the same as the corresponding ratio of the isomeric pair SiNC and SiCN produced under similar conditions. Silyl isocyanide is an excellent candidate for astronomical detection, because the spectroscopic and chemical properties are very similar to SiH$_3$CN which was recently identified in the circumstellar envelope of IRC+10216 by \citet{cernicharo_discovery_2017} and of SiNC and SiCN in the same source.