title: Barrierless proton transfer across weak CH⋯O hydrogen bonds in dimethyl ether dimer.
abstract: We present a combined computational and threshold photoelectron photoion coincidence study of two isotopologues of dimethyl ether, (DME - h6)n and (DME - d6)n n = 1 and 2, in the 9-14 eV photon energy range. Multiple isomers of neutral dimethyl ether dimer were considered, all of which may be present, and exhibited varying C-H⋯O interactions. Results from electronic structure calculations predict that all of them undergo barrierless proton transfer upon photoionization to the ground electronic state of the cation. In fact, all neutral isomers were found to relax to the same radical cation structure. The lowest energy dissociative photoionization channel of the dimer leads to CH3OHCH3 (+) by the loss of CH2OCH3 with a 0 K appearance energy of 9.71 ± 0.03 eV and 9.73 ± 0.03 eV for (DME - h6)2 and deuterated (DME - d6)2, respectively. The ground state threshold photoelectron spectrum band of the dimethyl ether dimer is broad and exhibits no vibrational structure. Dimerization results in a 350 meV decrease of the valence band appearance energy, a 140 meV decrease of the band maximum, thus an almost twofold increase in the ground state band width, compared with DME - d6 monomer.
authors: Laboratory of Physical Chemistry, ETH Zürich, Zürich 8093, Switzerland.
authors: Bruce L
authors: BL
authors: Yoder
authors: Department of Chemistry, Boston University, Boston, Massachusetts 02215-2521, USA.
authors: Ksenia B
authors: KB
authors: Bravaya
authors: Molecular Dynamics Group, Paul Scherrer Institut, Villigen 5232, Switzerland.
authors: Andras
authors: A
authors: Bodi
authors: Laboratory of Physical Chemistry, ETH Zürich, Zürich 8093, Switzerland.
authors: Adam H C
authors: AH
authors: West
authors: Department of Chemistry, University of the Pacific, Stockton, California 95211, USA.
authors: Bálint
authors: B
authors: Sztáray
authors: Laboratory of Physical Chemistry, ETH Zürich, Zürich 8093, Switzerland.
authors: Ruth
authors: R
authors: Signorell
mesh_terms: D002244:Carbon / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D003198:Computer Simulation; D019281:Dimerization; D006859:Hydrogen / Q000737:chemistry; D006860:Hydrogen Bonding; D007536:Isomerism; D008738:Methyl Ethers / Q000737:chemistry*; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry; D055668:Photochemical Processes; D056951:Photoelectron Spectroscopy; D017785:Photons; D011522:Protons; D013696:Temperature
chemical_list: D002412:Cations; D008738:Methyl Ethers; D011522:Protons; D002244:Carbon; D006859:Hydrogen; C033413:dimethyl ether; D010100:Oxygen