Nonadiabatic effects in substitutional isomers of Jahn-Teller molecules: The strange case of hydroxymethoxy

Abstract

The effects of nonadiabatic interactions attributable to a seam of conical intersections on the electronic structure of the 1,2(2)A states of hydroxymethoxy (HO)CH(2)O is explored. Illuminating comparisons are made between hydroxymethoxy and ethoxy and isopropoxy, all of which can be thought of as substitutional isomers of the methoxy radical. Surprisingly, the potential energy surfaces and conical topographies for hydroxymethoxy are shown to be dramatically different from those evidenced in ethoxy or isopropoxy radicals, dissimilarities traced to the hydroxyl group. Also considered in this study was the feasibility of representing the coupled 1,2(2)A adiabatic electronic states of hydroxymethoxy within the vibronic coupling approximation using a quasi-diabatic Hamiltonian and subsequently using that representation to simulate the photoelectron spectrum of the hydroxymethoxide anion. Complications attributable to the torsional motion of the hydroxyl hydrogen are analyzed.

Photoelectron spectroscopy of the hydroxymethoxide anion, H2C(OH)O−

“…A relaxed potential energy scan has a barrier to interconversion of 158 cm -1 for the ground 2 A state surface. This is lower than the multireference calculations from Dillon and Yarkony, 26 who report a barrier to interconversion of 361 cm -1 for the ground 2 A state, and with Eisfeld and Francisco, who report a barrier of at most 550 cm -1 for the 2 A state rotamer interconversion. The barrier to interconversion for the excited 2 A state is higher, at 968 cm -1 , which agrees very well with the multireference calculations from Dillon and Yarkony (993 cm -1 ).…”

“…48 The ground and first excited states of CH 2 (OH)O • , using the C s symmetry labels valid at HOCO = 0°, are described by 2 A and 2 A state labels. The molecular orbitals associated with the two lowest energy electronic states of H 2 C(OH)O • have also already been calculated, 11,26 and are associated with a half-filled a (a ) symmetry p y (p x ) orbital at the O1 atom for the ground (excited) electronic state (note: in this representation, the heavy atoms are taken to lie in the xz plane The lowest eBE peak in the spectrum, peak A, has a fwhm of 0.036 eV, a value close to the experimental resolution, suggesting minimal rotational broadening. See Section II.A for more details.…”

“…Although they pointed out that nonadiabatic effects might exist between the low-lying electronic states of H 2 C(OH)O • , they were not explicitly included in the calculations. 11 Dillon and Yarkony, 26 This work presents an anion photoelectron spectroscopic investigation of the hydroxymethoxy radical, as well as the measurement of its electron affinity (EA). Here, the ground 2 A and first excited The high reactivity of neutral H 2 C(OH)O • and its close relation to methanediol motivates its spectroscopic investigation through its negative ion, H 2 C(OH)O -, which is predicted to be more stable by 2.232 eV.…”

“…Previous experimental and theoretical work studied the effect of methyl substitutions, forming ethoxy, isopropoxy, and tert-butoxy radicals. [22][23][24][25][26][27] The substitution of a methyl group for a hydrogen atom will change the electronic structure of the methoxy radical, breaking its C 3v symmetry. For the ethoxy radical, significant Jahn-Teller distortions were observed in the CH 3 CH 2 O -photoelectron spectrum, where the CH 3 CH 2 O • state was found to be only 355 cm -1 higher in energy than the ground state.…”

“…22,27 While the work on interpreting the photoelectron spectra of the ethoxide anion yielded results that needed to be analyzed with the inclusion of Jahn-Teller distortions and vibronic coupling, 22,23,25,28 recent calculations suggest this will not be the case for hydroxymethoxy. 26 Eisfeld and Francisco 11 studied low lying electronic states of H 2 C(OH)O • , focusing on calculating its electronic absorption spectra (CASSCF/CASPT2, CASSCF/MRCI+Q). Although they pointed out that nonadiabatic effects might exist between the low-lying electronic states of H 2 C(OH)O • , they were not explicitly included in the calculations.…”