Reactivity, vibrational spectroscopy, internal rotation and thermochemical aspects of methylarsine

• Internal rotational, unimolecular rearrangement and hydrogen release pathways
• Methylarsine isomerization and H2-elimination kinetic rate constants
• Heat of formation and ionization energy of CH3AsH2 and CH2AsH3
• Frontier orbitals, partition coefficient, charge distribution and bond order indexes
• Harmonic and anharmonic frequency accuracies in reproducing experimental values

The aim of this investigation was to perform a characterization of the spectroscopic and thermodynamic properties of methylarsine (CH3AsH2). Post-Hartree-Fock, 29 DFT methods and eight different composite methodologies were employed in these analyses. A comparison between harmonic and anharmonic frequency accuracies in reproducing the observable frequencies was performed here. In addition, the CH3AsH2 → CH2AsH3 isomerization barrier energy was estimated in 100 kcal mol− 1, whereas the H2-release routes barrier heights were in the 45–107 kcal mol− 1 range. A rate constant of 10− 66 s− 1 was predicted regarding the isomerization route, while the CH2AsH3 hydrogen elimination mechanism is faster than the methylarsine one. The transition state structure of the CH3AsH2 internal rotational barrier energy varied between 1.0 and 1.4 kcal mol− 1. For the CH2AsH3 internal rotation the estimated barrier heights varied 0.6–2.5 kcal mol− 1. The adiabatic ionization energy and the heat of formation each structure was also calculated here.

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