Rotational Spectrum, Conformational Composition, Intramolecular Hydrogen Bonding, and Quantum Chemical Calculations of Mercaptoacetonitrile (HSCH₂C≡N), a Compound of Potential Astrochemical Interest

Abstract

The microwave spectra of mercaptoacetonitrile (HSCH2C≡N) and one deuterated species (DSCH2C≡N) were investigated in the 7.5-124 GHz spectral interval. The spectra of two conformers denoted SC and AP were assigned. The H-S-C-C chain of atoms is synclinal in SC and anti-periplanar in AP. The ground state of SC is split into two substates separated by a comparatively small energy difference resulting in closely spaced transitions with equal intensities. Several transitions of the parent species of SC deviate from Watson's Hamiltonian. Only slight improvements were obtained using a Hamiltonian that takes coupling between the two substates into account. Deviations from Watson's Hamiltonian were also observed for the parent species of AP. However, the spectrum of the deuterated species, which was investigated only for the SC conformer, fits satisfactorily to Watson's Hamiltonian. Relative intensity measurements found SC to be lower in energy than AP by 3.8(3) kJ/mol. The strength of the intramolecular hydrogen bond between the thiol and cyano groups was estimated to be ∼2.1 kJ/mol. The microwave work was augmented by quantum chemical calculations at CCSD and MP2 levels using basis sets of minimum triple-ζ quality. Mercaptoacetonitrile has astrochemical interest, and the spectra presented herein should be useful for a potential identification of this compound in the interstellar medium. Three different ways of generating mercaptoacetonitrile from compounds already found in the interstellar medium were explored by quantum chemical calculations.

A theoretical study on the spectroscopy, structure, and stability of C2H3NS molecules

“…More decomposition products were reported for CH 3 SCN subjected to electric discharges [21]. Recently, Møllen-dal and collaborators measured the gas-phase rotational spectroscopy of mercaptoacetonitrile, another isomer of C 2 H 3 NS stoichiometry [22]. From this study, we know that mercaptoacetonitrile has two conformers with a calculated energetic separation between them of 4.68 kJ/mol [22].…”

“…Available experimental values, concerning the vibrationless states of species 1, 2 and 3 [22,62,63], allow estimation of the precision of these predictions. Absolute differences between experimental and theoretical values are 0.4 and 0.2 %, for C 0 and B 0 of 3, respectively.…”

“…Tables 3, 4, 5 and 6 (see Online Resource for their full versions) collect information concerning the vibrational spectroscopy of molecules 1, 2, 3, and 9 for Equilibrium electric dipole moment and polarizability values derived using CCSD/cc-pVTZ are also given a Experimental value [22] b Based on CCSD(T) calculations of Ref. [25] c Experimental value [62] A e /GHz B e /GHz which experimental values are also available.…”

“…Recently, Møllen-dal and collaborators measured the gas-phase rotational spectroscopy of mercaptoacetonitrile, another isomer of C 2 H 3 NS stoichiometry [22]. From this study, we know that mercaptoacetonitrile has two conformers with a calculated energetic separation between them of 4.68 kJ/mol [22]. To the best of our knowledge, no experimental data are available for the isomerisation reactions of C 2 H 3 NS family members.…”

Photochemistry of XCH2CN (X = −Cl, −SH) in Argon Matrices

“…Of the three lowest energy C 2 H 3 SN family members, mercaptoacetonitrile (HS-CH 2 -CN), which has a weak chemical stability at room temperature, is the only one not commercially available and is therefore less well studied. Nevertheless, this species has been explicitly discussed as a likely astrochemical species whose potential routes of formation in the interstellar medium were explored and microwave spectrum experimentally measured at both -30 °C and room temperature 21 . Synclinal and antiperiplanar conformers of mercaptoacetonitrile were identified and their energetic separation measured to be 3.8±0.3 kJ/mol.…”