Giannoula Theodorakopoulos

MRD CI calculations on the asymmetric stretch potentials of H2O in the ground and the first seven singlet excited states

Abstract Cross sections of the potential energy surfaces of the H 2 O molecules in the first eight singlet states have been generated for the elongation of one of the OH bonds, Keeping the other fixed and for different values of the HOH bond angle. Only the first 1 A″ (Ā 1 B 1 ) and the first excited 1 A′ (B 1 A 1 ) states are found to be dissociative along such cross sections. Several previously unreported conical intersections are noted, one between the 3 1 A′ and 4 1 A′ states and another between the 2 1 A″ and 3 1 A″ species. The OH + H( 2 S) disociation limits for the lowest eight water singlet states are identified, the highest three of which correspond to OH π → 3s and 3p Rydberg excitations.

Bending potentials for H2O in the ground and the first six singlet excited states

Abstract MRD CI calculations are presented for the bending potentials of H 2 O in the ground and first six singlet excited states. The results are discussed with reference to the H( 2 S) + OH(A 2 Σ + ) dissociation path of H 2 O.

Potential energy surfaces for the photodissociation H2O→O(1Dg + H2(X1Σ+g)

Abstract The minimum energy pathways for symmetrical dissociation of water into O( 1 D g + H 2 ( X 1 Σ + g ) are calculated by the MRD Cl technique for various excited states of H 2 O and possible mechanism for the photodissociation are discussed.

Amplified Halogen Bonding in a Small Space

Weak, intermolecular forces are difficult to observe in solution because the molecular encounters are random, short-lived, and overwhelmed by the solvent. In confined spaces such as capsules and the active sites of enzymes or receptors, the encounters are prolonged, prearranged, and isolated from the medium. We report here the application of encapsulation techniques to directly observe halogen bonding. The small volume of the capsule amplifies the concentrations of both donor and acceptor, while the shape of the space permits their proper alignment. The extended lifetime of the encapsulation complex allows the weak interaction to be observed and characterized by conventional NMR methods under conditions in which the interaction would be negligible in bulk solvent.

MRD-CI calculations on the potential energy curves of the ground and excited electronic states of the noble-gas hydrides, HeH, NeH and ArH

MRD-CI calculations have been carried out for the ground- and some excited-state potential curves of He+H, Ne+H and Ar+H. Deep minima are obtained for the excited states at internuclear distances similar to those of the corresponding cations. The B2 Pi to A2 Sigma + computed transition energies do not support a previous assignment to this transition in ArH, at 7670 AA.

Nonorthonormal CI for molecular excited states. I. The sudden polarization effect in 90° twisted ethylene

The accurate and efficient calculation of properties of excited states, especially those involved in near‐degeneracies and valence‐Rydberg mixings, may depend crucially on the zeroth order orbitals employed for the description of a few important configurations. When self‐consistent field orbitals specific for the states of interest are employed, one becomes involved with nonorthonormal basis sets, which circumstance has conceptual as well as computational implications. In this work, we have developed a nonorthonormal configuration interaction (NONCI) method and have applied it to the calculation of the ‘‘sudden polarization’’ effect in the zwitterionic excited states of ethylene, in the spirit of a state‐specific theory. A very small NONCI, (6×6), yields similar results to those from previous large CI calculations. In particular, the sudden rise of the dipole moment as a function of the pyramidalization angle of the CH2 group of the 90° twisted Z state is predicted while it is shown that the inclusion of ...

A non-van der Waals minimum of the He(1S) + H2(B 1Σu+) excited surface

Abstract We have carried out MRD CI calculations for the first excited state of HeH 2 ( 1 A′) at geometries which have He( 1 S) approaching the center of mass of H 2 (B 1 Σ u + ) at 45°. The calculated energies yield a barrier of 0.24 eV and a minimum of 1.5 eV. This minimum occurs near an avoided crossing with the ground-energy surface which is not found for collinear or perpendicular geometries. These results suggest an explanation for the electronic quenching of HD(B 1 Σ u + ) in the presence of He observed by Moore and co-workers.

Excited-State Intramolecular Proton Transfer in Hydroxyoxime-Based Chemical Sensors

The electronic structure of a series of β-hydroxy-oximes, with different aromatic cores (naphthalene, pyrene, coumarin, pyridine) between the oxime and the hydroxyl groups, has been investigated by time-dependent density functional theory (TDDFT) and of the naphthalene-based oxime, in addition, by resolution-of-identity second-order perturbative coupled cluster (RICC2) calculations with basis sets up to augmented triple-ζ quality. The particular systems have been proposed as fluorescent sensors of organophosphorus (OP) nerve agents, with enhancement of fluorescence accompanying the sensing of OP agents. It is found that the experimentally observed fluorescence quenching of the oxime sensors in their initial form can be attributed to intramolecular proton transfer upon excitation from the β-hydroxyl group to the nitrogen atom, thus forming a weakly emitting hydroxylaminoquinoid.

Theoretical dipole transition moments for transitions between bound electronic states and non-adiabatic coupling matrix elements between 2Σ+ of HeH

Dipole transition moments and radial non-adiabatic coupling matrix elements between electronic states of HeH are presented. The estimated radiative lifetimes of the excited states of HeH are in good agreement with the available experimental data.

Theoretical dipole transition moments for the transitions to the ground state X2σ+ from the A2σ+, B2Π, C2σ+, D2σ+ and E2Π states and for the B 2?A 2:+ system in HeH

Dipole transition moments have been calculated for the transitions A2+ to X2+, B2 to X2+, C2+ to X2+, D2+ to X2+, E2 to X2+ and B2 to A2+ in HeH. The spectroscopic constants obtained in this work support an experimental assignment for the C 2+ to A 2+ transition.