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A combined theoretical and experimental approach to the unimolecular loss of molecular hydrogen from protonated formaldehyde: Determination of the average internal energy of metastable [CH 2 OH] + ions
Author(s) -
Hvistendahl Georg,
Uggerud Einar
Publication year - 1991
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210260204
Subject(s) - chemistry , metastability , protonation , kinetic isotope effect , kinetic energy , ab initio , intramolecular force , ion , quantum tunnelling , hydrogen , potential energy surface , proton , hydrogen atom , internal energy , formaldehyde , potential energy , atomic physics , computational chemistry , thermodynamics , deuterium , materials science , physics , stereochemistry , organic chemistry , alkyl , optoelectronics , quantum mechanics
Ab initio quantum chemical calculations (MP2/4–31G**) were performed for the dihydrogen elimination reaction from protonated formaldehyde. The energy difference between reactants and products and the activation energies were found to be in good agreement with the corresponding experimental quantities. Theoretical rate vs. energy curves were computed for a series of isotopic variants of the reaction using the Rice–Ramsperger–Kassel–Marcus (RRKM) method. The vibrational frequencies used in these calculations were taken from the 4–31G** geometry‐optimized transition state and reactant structures. Quantum mechanical tunnelling was introduced to explain the existence of metastable CH 2 OH ions, and a negative kinetic shift of about 0.1 eV was found. The intramolecular kinetic isotope effect for loss of HH/HD and DH/DD was calculated and compared with the experimental data. The result is consistent with the assumption that the average internal energy of metastable [CH 2 OH] + ions is very close to the critical energy for H 2 loss.