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Large amplitude vibrations of acetyl isocyanate, methyl cyanoformate, and acetyl cyanate

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Abstract

The far infrared region of three detectable molecules sharing the empirical formula C3H3O2N, acetyl isocyanate CH3CONCO (AISO), methyl cyanoformate NC–COOCH3 (MCN) and acetyl cyanate CH3COOCN (ACN), is explored using explicitly correlated coupled cluster ab initio methods and a variational procedure designed for non-rigid species and large amplitude motions. The three isomeric forms display two conformers, cis and trans, of Cs symmetry that intertransform through the torsion of the central bond. This internal rotation interacts with the methyl group torsion generating a ground electronic state potential energy surface of six minima. Accurate rotational constants, centrifugal distortion constants, potential energy barriers, and surfaces, as well as, the low energy levels and their splittings, are provided. Far infrared energies are calculated up to 600 cm−1 which represent excitations of the torsional and the skeletal bending modes. Below 410 cm−1, 28, 14 and 20 vibrational energy levels and their splittings have been identified and classified for acetyl isocyanate, methyl cyanoformate, and acetyl cyanate, respectively. All the methyl torsion barriers are relatively low (∼300 cm−1) generating relevant tunneling effects. Computed spectroscopic parameters can help further interpretation and assignments of experimental rotational spectra using effective Hamiltonians.

Graphical abstract: Large amplitude vibrations of acetyl isocyanate, methyl cyanoformate, and acetyl cyanate

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Publication details

The article was received on 16 Jul 2018, accepted on 19 Sep 2018 and first published on 19 Sep 2018


Article type: Paper
DOI: 10.1039/C8CP04490B
Citation: Phys. Chem. Chem. Phys., 2018, Advance Article
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    Large amplitude vibrations of acetyl isocyanate, methyl cyanoformate, and acetyl cyanate

    S. Dalbouha and M. L. Senent, Phys. Chem. Chem. Phys., 2018, Advance Article , DOI: 10.1039/C8CP04490B

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