title: Timescales of N-H bond dissociation in pyrrole: a nonadiabatic dynamics study.
abstract: The excitation wavelength dependent photodynamics of pyrrole are investigated by nonadiabatic trajectory-surface-hopping dynamics simulations based on time dependent density functional theory (TDDFT) and the algebraic diagrammatic construction method to the second order (ADC(2)). The ADC(2) results confirm that the N-H bond dissociation occurring upon excitation at the origin of the first excited state, S1(πσ*), is driven by tunnelling [Roberts et al., Faraday Discuss., 2013, 163, 95] as a barrier of ΔE = 1780 cm(-1) traps the population in a quasi-bound minimum. Upon excitation to S1(πσ*) in the wavelength range of 236-240 nm, direct dissociation of the N-H bond takes place with a time constant of 28 fs. The computed time constant is in very good agreement with recently reported measurements. Excitation to the lowest B2 state in the 198-202 nm range returns a time constant for N-H fission of 48 fs at the B3LYP/def2-TZVPD level, in perfect agreement with the experiment [Roberts et al. Faraday Discuss., 2013, 163, 95]. For the same wavelength range the ADC(2)/aug-cc-pVDZ decay constant is more than three times longer than the experimentally reported one. The accuracy of the B3LYP/def2-TZVPD dynamics is checked against reference complete-active-space second-order perturbation theory (CASPT2) calculations and explained in terms of correct topography of the ππ* surface and the lack of mixing between the ππ* and the 3px Rydberg states which occurs in the ADC(2) method.
authors.affiliation: Department of Physical Chemistry, Ruđer Bošković Institute, HR-10000 Zagreb, Croatia. nadja.doslic@irb.hr.
authors.forename: Marin
authors.initials: M
authors.lastname: Sapunar
authors.forename: Aurora
authors.initials: A
authors.lastname: Ponzi
authors.forename: Sermsiri
authors.initials: S
authors.lastname: Chaiwongwattana
authors.forename: Momir
authors.initials: M
authors.lastname: Mališ
authors.forename: Antonio
authors.initials: A
authors.lastname: Prlj
authors.forename: Piero
authors.initials: P
authors.lastname: Decleva
authors.forename: Nađa
authors.initials: N
authors.lastname: Došlić