Multistate, multichannel coupled diabatic state representations of adiabatic states coupled by conical intersections. CH2OH photodissociation

Abstract

A coupled diabatic state representation, H, of the 1, 2, 3 A states of CHOH suitable for the description of the three channel, three state photodissociation process CHOH(1 A) + hv → CHOH(2, 3 A) → CHO(X, A) + H, cis-CHOH + H, trans-CHOH + H, is reported. The representation is based on electronic structure data (energies, energy gradients, and derivative couplings) obtained exclusively from multireference configuration interaction single and double excitation wave functions. Diabat shifting is employed to improve the representation's agreement with accurate experimental energetics. A careful analysis of the numerous minima, saddle points, and conical intersection seams is reported. The computed T(3 A) ∼ 35 220 cm is in excellent agreement with the experimental estimate of 35 053 cm, and the computed channel dissociation energies, D, for CHO 9453 (10 160), cis-HCOH 30 310.2 (29 923), and trans-HCOH 28 799 (28 391) cm are in good accord with the measured values given parenthetically. These accurate energetics over a wide range of nuclear configurations strongly support the ability of this H to enable quality simulations of nonadiabatic dynamics.

Photoinduced C–H bond fission in prototypical organic molecules and radicals

“…207 These findings have been rationalised by assuming initial excitation to both the 3 2 A (3p) and 2 2 A (3s) Rydberg states, the former of which can decay by passage through successive conical intersections in the RC-H stretch coordinate en route to both cis-and trans-HCOH products in their respective ground states. 208 The corresponding 3sn absorption of the 1-hydroxyethyl (CH3CHOH) radical extends to  > 500 nm. As with the CH2OH radical, studies involving selectively deuterated precursors and long excitation wavelengths identify O-H bond fission (leading to fast H atoms with an anisotropic recoil velocity distribution along with CH3CHO co-products) as the exclusive fragmentation channel, and theory 209 has again identified a conical intersection between the 2 2 A ( 2 n(3s/*)) and 1 2 A (ground state) PESs in the RO-H stretch coordinate that successfully explains this observation.…”

Up to a Sign. The Insidious Effects of Energetically Inaccessible Conical Intersections on Unimolecular Reactions

“…In a previous theoretical simulation of the unimolecular reaction, only the D 0 PES was used, and the GP effect and DBOC were ignored. We undertook a quantum dynamical study of the unimolecular reaction using a reduced-dimensional model including the O–H ( R ) and C–O bonds, the C–O–H angle, and the H–C–O–H torsional angle (ϕ), on the ab initio based diabatic PEM. , Interestingly, the overtone lifetimes immediately above the dissociation limit were found to be insensitive to the incorporation of the GP. A detailed analysis revealed that the tunneling paths through the equivalent saddle points on each side of the CI repel each other (see Figure ), due to the repulsive topography of the PES along ϕ.…”

“…We undertook a quantum dynamical study 70 71 on the ab initio based diabatic PEM. 72,73 Interestingly, the overtone lifetimes immediately above the dissociation limit were found to be insensitive to the incorporation of the GP. A detailed analysis revealed that the tunneling paths through the equivalent saddle points on each side of the CI repel each other (see Figure 5), due to the repulsive topography of the PES along ϕ.…”

Nonadiabatic Dynamics in Photodissociation of Hydroxymethyl in the 32A(3px) Rydberg State: A Nine-Dimensional Quantum Study

“…In this work, we use a full 9D model to study the absorption spectrum of CH 2 OH (3p x ) based on the three-state diabatic PEM constructed by Malbon and Yarkony . The nuclear Hamiltonian of the system in the diabatic representation is given as follows: in which Η d,(3) is the 3 × 3 diabatic PEM.…”