Thermal decomposition of formic acid in the gas phase: bimolecular and H2O catalysed reactions

• Published in: Molecular physics Vol. 92; no. 3; pp. 581 - 586
• Main Authors: TOKMAKOV, By I. V., HSU, C.-C., LIN, L. V. MOSKALEVA and M. C.
• Format: Journal Article
• Language: English
• Published: Taylor & Francis Group 01.10.1997
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/002689797170329

The thermal decomposition of formic acid in the gas phase by a bimolecular self-reaction and by two H 2 O catalysed processes has been investigated by ab initio molecular orbital calculations using a modified Gaussian 2 (G2M) method, which has been tested for the present system with calculations for the geometry and stability of the dimer, (HCOOH) 2 , formed by the hydrogen bonding of two Z conformers. The dissociation energy for the dimer was calculated to be 13·9 kcalmol, which agrees closely with the experimental values, 12-15 kcal mol -1 , and the result of a high-level ab initio calculation. The energy barrier for the self-reaction involving two Z conformers via transition state 1, producing 2H 2 O + 2CO, was found to be 67·9 kcal mol -1 . The value is much greater than those for the H 2 catalysed decomposition of the Z conformer via transition state 2, producing H 2 O + CO + H 2 O, 48·2 kcal mol -1 , and the H 2 O catalysed decomposition of the E conformer via transition state 3, producing H 2 + CO 2 + H 2 O, 44·2 kcal mol -1 . Thermal rate constants for these processes, covering the 200-1000K temperature range, have been calculated with and without tunnelling corrections.