Photoelectron Spectrum and Dynamics of the Uracil Cation

Abstract

The photoelectron spectrum of uracil and the molecular dynamics of its radical cation are investigated using the multiconfigurational time-dependent Hartree (MCTDH) method. For this aim, the vibronic coupling model Hamiltonian is used including up to ten important a' modes. Moreover, to account for coupling through conical intersections between states of different symmetry in the system, coupling constants of two a″ modes are taken into account. The parameters used in the model are obtained by fitting to ab inito data obtained with extensive EOM-IP-CCSD calculations. The first four cationic states were investigated, which are either of A″ (hole in a π orbital) or A' (hole in a nO orbital) symmetry. The results of the wavepacket propagations were used to calculate the corresponding photoelectron spectrum and compare to the experimental spectrum. The MCTDH simulations reproduce the experimental spectrum well. The dynamics starting from the D2 and D3 ionic states show a fast relaxation to the cationic ground state often involving direct D2-D0 or D3-D1 transitions.

Ultraviolet relaxation dynamics in uracil: Time-resolved photoion yield studies using a laser-based thermal desorption source

“…We note that non-adiabatic relaxation dynamics have recently been investigated theoretically in the uracil cation and these studies predict extremely rapid internal conversion to the D0 ground state occurs before significant fragmentation takes place. 53,54…”

Ultrafast and radiationless electronic excited state decay of uracil and thymine cations: computing the effects of dynamic electron correlation

“…Several studies in the literature have focused on the accurate characterisation of the ionisation potentials (both vertical and adiabatic) of DNA nucleobases, 15 which are strongly modulated due to solvation, [6][7][8] while less work has been done in the characterisation of the doublet excited state reactivity. Matsika and co-workers have analysed theoretically the role of the different excited cationic states taking part in the photoionisation of uracil from both static [16][17][18][19] and dynamic 20,21 standpoints, including also their subsequent fragmentation. 22 These studies shown that, upon photoionisation, a majority of the population will reach the more favourable D 2 ( 2 π + HOMO−1 ) state, which will then rapidly decay to D 1 ( 2 n + O ) and then reach D 0 ( 2 π + HOMO ) within 100 fs.…”

Computing the Ultrafast and Radiationless Electronic Excited State Decay of Cytosine and 5‐methyl‐cytosine Cations: Uncovering the Role of Dynamic Electron Correlation

“…The ionisation of cytosine derivatives has been a topic of scarce study in the literature, with the only references found by us being relative to the specific UV/Vis absorption spectral fingerprints of cytosine +[22] as well as their IR features . Very little is also known about the cationic excited state decay relaxation, particularly comparing to other similar systems like the RNA nucleobase uracil . The only works available in the literature are characterisation of the Dyson norms of cytosine and the evolution of the cationic manifold along the relaxation of the bright and initially accessed singlet decay channel by Matsika and co‐workers, which cover different facets of potential ionisation mechanisms while not depicting the actual cation generation and its excited state decay relaxation channels.…”