Issue 28, 2011

Dissociative photoionization mechanism of methanol isotopologues (CH3OH, CD3OH, CH3OD and CD3OD) by iPEPICO: energetics, statistical and non-statistical kinetics and isotope effects

Abstract

The dissociative photoionization of energy selected methanol isotopologue (CH3OH, CD3OH, CH3OD and CD3OD) cations was investigated using imaging Photoelectron Photoion Coincidence (iPEPICO) spectroscopy. The first dissociation is an H/D-atom loss from the carbon, also confirmed by partial deuteration. Somewhat above 12 eV, a parallel H2-loss channel weakly asserts itself. At photon energies above 15 eV, in a consecutive hydrogen molecule loss to the first H-atom loss, the formation of CHO+/CDO+ dominates as opposed to COH+/COD+ formation. We see little evidence for H-atom scrambling in these processes. In the photon energy range corresponding to the [B with combining tilde] and [C with combining tilde] ion states, a hydroxyl radical loss appears yielding CH3+/CD3+. Based on the branching ratios, statistical considerations and ab initio calculations, this process is confirmed to take place on the first electronically excited Ã2A′ ion state. Uncharacteristically, internal conversion is outcompeted by unimolecular dissociation due to the apparently weak Renner–Teller-like coupling between the [X with combining tilde] and the à ion states. The experimental 0 K appearance energies of the ions CH2OH+, CD2OH+, CH2OD+ and CD2OD+ are measured to be 11.646 ± 0.003 eV, 11.739 ± 0.003 eV, 11.642 ± 0.003 eV and 11.737 ± 0.003 eV, respectively. The E0(CH2OH+) = 11.6454 ± 0.0017 eV was obtained based on the independently measured isotopologue results and calculated zero point effects. The 0 K heat of formation of CH2OH+, protonated formaldehyde, was determined to be 717.7 ± 0.7 kJ mol−1. This yields a 0 K heat of formation of CH2OH of −11.1 ± 0.9 kJ mol−1 and an experimental 298 K proton affinity of formaldehyde of 711.6 ± 0.8 kJ mol−1. The reverse barrier to homonuclear H2-loss from CH3OH+ is determined to be 36 kJ mol−1, whereas for heteronuclear H2-loss from CH2OH+ it is found to be 210 kJ mol−1.

Graphical abstract: Dissociative photoionization mechanism of methanol isotopologues (CH3OH, CD3OH, CH3OD and CD3OD) by iPEPICO: energetics, statistical and non-statistical kinetics and isotope effects

Article information

Article type
Paper
Submitted
01 Apr 2011
Accepted
31 May 2011
First published
20 Jun 2011

Phys. Chem. Chem. Phys., 2011,13, 13009-13020

Dissociative photoionization mechanism of methanol isotopologues (CH3OH, CD3OH, CH3OD and CD3OD) by iPEPICO: energetics, statistical and non-statistical kinetics and isotope effects

S. Borkar, B. Sztáray and A. Bodi, Phys. Chem. Chem. Phys., 2011, 13, 13009 DOI: 10.1039/C1CP21015G

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements