RASPT2 Analysis of the F^–(H₂O)_n=1–7 and OH^–(H₂O)_n=1–7 CTTS States

Abstract

We analyze the electronic structure of the lowest excited states of the F(HO) and OH(HO) anionic clusters in the framework of RASPT2 theory. At the ground-state geometry, these clusters can bind the excess electron in the first excited singlet and triplet states for n ≥ 3 for F and n ≥ 2 for OH. The geometry relaxation of the F(HO) clusters in their lowest-energy triplet state produces two series of minima. A first series is made of a F radical weakly bound to a negatively charged water cluster to form F-(HO) . A second series associated with hydrogen transfer from a water molecule to the fluorine atom is built on a HF molecule and a OH radical bound to a negatively charged water cluster to form OH-HF-(HO) . This second series provides the lowest-energy isomers of F(HO) for the excited state. These two series of minima are inherited from the neutral fluorine water cluster structure only weakly perturbed by the excess electron. They are similar to the OH(HO) isomers obtained for the lowest-energy triplet state, which are also made of a neutral OH radical inserted in the water molecule network of a (HO) cluster. For all of these clusters in the lowest-energy excited state, the excess electron is localized outside of the cluster near unbound hydrogen atoms. Its binding energy is well correlated to the electric dipole of the cluster, and a lower limit of 4.1 D is necessary to bind it to the cluster. The two series of F(HO) isomers offer two very different routes for geminate recombination observed in water solutions. Our calculation suggests that the recombination takes place with the OH radical left after hydrogen transfer rather than with the F radical.

Anomalous Intrinsic Fluorescence of HCl and NaOH Aqueous Solutions

“…A similar result is also obtained for the NaOH model where we observe the formation of the OH radical with the concomitant dissociation of a H atom from the cluster surface at the CI to the ground state. This behavior is in agreement with what is observed for small OH – water cluster. , …”

“…This behavior is in agreement with what is observed for small OH − water cluster. 51,56 To account for fluorescence, we have been inspired by the suggestions that come from recent literature, according to which water molecules could be able to trap the excited state due to defects in the hydrogen bond network, 57 thus preventing the nonradiative S 1 decay. 55 To simulate this latter situation, we constrained the atoms that belong to the cluster surface and carried out the same S 1 geometry optimization.…”

Microsolvation of the Be-F bond in complexes of BeF2, BeF3–1, and BeF4–2with nH2O, forn = 1–6

“…Spin-spin coupling constants for the complexes were evaluated using the equation-of-motion coupled cluster singles and doubles (EOM-CCSD) method in the CI (configuration interaction)-like approximation [46,47] with all electrons correlated. For these calculations, the Ahlrichs qzp basis set [48] was placed on 17 O and 19 F, the Dunning cc-pVDZ basis set on 1 H atoms, and the hybrid basis set developed previously on 9 Be [49]. All terms which contribute to the total coupling constant, namely, the paramagnetic spin orbit (PSO), diamagnetic spin orbit (DSO), Fermi contact (FC), and spin dipole (SD), have been evaluated.…”

“…The one-bond coupling constants 1 J(Be-F) in the complexes of BeF 2 , BeF 3 -1 , and BeF 4 -2 with H 2 O are always negative since the magnetogyric ratio of 9 Be is negative. 5 which is a plot of 1 J(Be-F) versus the Be-F distance.…”

“…The polar character of water leads to the dissociation of salts in aqueous solution and the dispersion of the resulting ions. The solvation of anions through hydrogen bonding in aqueous solution [2] has been investigated theoretically for a number of anions [3,4], including Fand Cl - [5][6][7][8][9], BF 4 - [10] and PF 6 - [11]. Among the myriad of possible anions, we have turned our attention to BeF 3 -1 and BeF 4 -2 .…”