Spectroscopic signatures of proton transfer dynamics in the water dimer cation

Abstract

Using full dimensional EOM-IP-CCSD/aug-cc-pVTZ potential energy surfaces, the photoelectron spectrum, vibrational structure, and ionization dynamics of the water dimer radical cation, (H 2 O) + 2 , were computed. We also report an experimental photoelectron spectrum which is derived from photoionization efficiency mea- Hamiltonian was used to compute the ionization dynamics for both the ground state and first excited state of the cation. The dynamics show markedly different behavior and spectroscopic signatures depending on which state of the cation is accessed by the ionization. Ionization to the ground-state cation surface induces a hydrogen transfer which is complete within 50 femtoseconds, whereas ionization to the first excited state results in a much slower process.

Ionization of Water Clusters Mediated by Exciton Energy Transfer from Argon Clusters

“…34,35 Finally we discuss the nature of the excitation process that is occurring in these mixed 16 The protonated cluster appearance energies agree well with those measured earlier 2 but the photoionization efficiency curve follows the shape of the argon cluster absorption spectrum quite dramatically. This is reflected in the enhancement of signal around 11.5 eV, peaking at 11.92 eV, dropping down and then rising again.…”

“…4 Theory has shown that the structure of the water cluster ions are very different from their neutral ground state geometries, and gives rise to poor Franck-Condon (FC) factors, leading to a vibrationally excited cluster ion upon vertical excitation. 4,16,[36][37][38] This vibrationally excited cluster ion will rearrange via proton transfer to form a complex of the form (H 3 O) + OH in the case of the dimer, and it is stable to dissociation at threshold. Indeed, the non-fragmented dimer has been observed in photoionization experiments, 16,39 where at the appearance of (H 3 O) + at 11.71 eV is reflected directly in a lowering of signal of (H 2 O) 2 + .…”

“…15 The reported appearance energies for the non-protonated and protonated dimer and trimer were all consistently below literature values (by about 0.3-0.5 eV) and this discrepancy was recently discussed. 2, 16 Jongma et al carried out an extensive reflectron time-of-flight (TOF) analysis of the fragmentation of water clusters in an argon expansion which was photoionized with VUV light (12.2 and 13.4 eV). 17 They saw evidence for the formation of "unprotonated" water clusters and suggested that upon ionization, water clusters take the form…”

The effect of microhydration on ionization energies of thymine

“…This method has been successfully applied to describe electronic structure of ionized benzene dimers [31,33], water clusters [34][35][36] and dimers of nucleobases [3-5, 7, 8].…”

Proton transfer or hemibonding? The structure and stability of radical cation clusters

“…While there has been a large number of studies devoted to study these systems, they have predominantly focused on dimers. [2][3][4][5][6][7][8][9][10][11][13][14][15][16][17][18][20][21][22][25][26][27] The most extensively studied radical cation cluster is (H 2 O) 2 . + , and a wide variety of methods have been applied to characterise its structure.…”