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Spectroscopy of the Simplest Criegee Intermediate CH 2 OO: Simulation of the First Bands in Its Electronic and Photoelectron Spectra
Author(s) -
Lee Edmond P. F.,
Mok Daniel K. W.,
Shallcross Dudley E.,
Percival Carl J.,
Osborn David L.,
Taatjes Craig A.,
Dyke John M.
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201200848
Subject(s) - photoionization , chemistry , electronic structure , absorption spectroscopy , photoemission spectroscopy , atomic physics , ab initio quantum chemistry methods , ionization , spectral line , x ray photoelectron spectroscopy , configuration interaction , computational chemistry , ion , molecule , physics , nuclear magnetic resonance , organic chemistry , quantum mechanics , astronomy
Abstract CH 2 OO, the simplest Criegee intermediate, and ozone are isoelectronic. They both play very important roles in atmospheric chemistry. Whilst extensive experimental studies have been made on ozone, there were no direct gas‐phase studies on CH 2 OO until very recently when its photoionization spectrum was recorded and kinetics studies were made of some reactions of CH 2 OO with a number of molecules of atmospheric importance, using photoionization mass spectrometry to monitor CH 2 OO. In order to encourage more direct studies on CH 2 OO and other Criegee intermediates, the electronic and photoelectron spectra of CH 2 OO have been simulated using high level electronic structure calculations and Franck–Condon factor calculations, and the results are presented here. Adiabatic and vertical excitation energies of CH 2 OO were calculated with TDDFT, EOM‐CCSD, and CASSCF methods. Also, DFT, QCISD and CASSCF calculations were performed on neutral and low‐lying ionic states, with single energy calculations being carried out at higher levels to obtain more reliable ionization energies. The results show that the most intense band in the electronic spectrum of CH 2 OO corresponds to the ${{\rm{\tilde B}}}$ 1 A′ ← ${{\rm{\tilde X}}}$ 1 A′ absorption. It is a broad band in the region 250–450 nm showing extensive structure in vibrational modes involving O–O stretching and C‐O‐O bending. Evidence is presented to show that the electronic absorption spectrum of CH 2 OO has probably been recorded in earlier work, albeit at low resolution. We suggest that CH 2 OO was prepared in this earlier work from the reaction of CH 2 I with O 2 and that the assignment of the observed spectrum solely to CH 2 IOO is incorrect. The low ionization energy region of the photoelectron spectrum of CH 2 OO consists of two overlapping vibrationally structured bands corresponding to one‐electron ionizations from the highest two occupied molecular orbitals of the neutral molecule. In each case, the adiabatic component is the most intense and the adiabatic ionization energies of these bands are expected to be very close, at 9.971 and 9.974 eV at the highest level of theory used.