Gabriel J. Vazquez

The electronic structure of HO2

Bending and stretching potential energy curves of twelve electronic states of HO2 + are calculated using the MRD-CI formalism. The basis set is of double-zeta plus polarization quality augmented with s- and p-type bond and Rydberg functions. The HO2 vertical ionization energies are reported and compared with the approximate HO2 + vertical excitation spectra. The first excited ionic state 1 1 A′(2a″)-1 is found to lie some 0·3 eV above the X 3 A″(7a′)-1 ground cationic state. The electronic structure and relevant features of the electronic states are discussed. The dissociation energies of the O-OH and OO-H bonds in the ground state of the ion and the neutral molecule are calculated and the O2 proton affinity is estimated.

Adiabatic versus diabatic descriptions of the lowest Rydberg and valence Σ+1 states of HCl

In this contribution we first report new ab initio self-consistent field configuration interaction calculations of the first excited adiabatic potential of (1)Σ(+) symmetry, the 2(1)Σ(+) or B(1)Σ(+) state, which presents two minima and can thus be seen as made up of the Rydberg E(1)Σ(+) and the valence V(1)Σ(+) states. Based on the computed 2(1)Σ(+) potential, we devised a theoretical procedure to compute the vibronic structure in order to try to explain the energy levels observed in the region above 76 254.4 cm(-1) which display an irregular vibrational structure, indicative of spectral perturbations. We try to find out which representation of the electronic states, the diabatic or the adiabatic one, is best suited to replicate the lowest observed vibronic levels of the E and V states. To this end, we deduce, from the 2(1)Σ(+) potential and its complementary adiabatic potential, two diabatic potentials. We then carry out a coupled equation treatment based on these diabatic potentials. The results of this treatment indicate that, in the present case, the adiabatic representation is better than the diabatic one to describe the observed vibronic levels. This is due, as expected, to the existence of a strong electrostatic interaction between the two diabatic potentials.

Multireference singles and doubles configuration interaction study of the photoelectron spectrum of HO−2

Multireference singles and doubles configuration interaction (MRD‐CI) electronic structure calculations are carried out on the hydroperoxyl radical and its negative ion. Potential energy curves of the ground state of the anion and of the ground and first excited states of the neutral molecule along the O–OH coordinate are employed to compute the Franck–Condon factors for the electron photodetachment processes HO2(X 2A‘,A 2A’)+e←HO−2(X 1 A’). The theoretical spectrum agrees fairly well with the photoelectron spectrum reported by Oakes, Harding, and Ellison, and is consistent with their assignment of the peaks K and D as origins for the electron loss transitions to the HO2 A and X states, respectively. An alternative choice of peak E as X←X− origin yields better agreement between computed and experimental Franck–Condon factors than does the peak D assignment, but is less satisfactory when energetic considerations are taken into account. Two independent ab initio results lend support to the value of 1.078±0....

MRD CI study of the electron affinity of HO2 and the photodetachment energy of HO2

Abstract Extended ab initio MRD CI electronic structure calculations are carried out on the ground state of HO2− and on the ground and first excited states of HO2. Cuts of the potential energy surfaces along the OOH, bending and OOH coordinates are calculated in the neighbourhood of the equilibrium position and employed to compute the equilibrium geometry and fundamental vibrational frequencies of HO2−. Systematic calculations on the OO−, OHOH−, O2O2− and HO2 HO2− neutral-anion pairs indicate that the theoretical calculations underestimate the electron affinities by a nearly constant amount. Accordingly the EA (HO2) is estimated to be 1.069±0.05 eV which is in good agreement with the measured value of 1.078 eV obtained from the HO2− photoelectron spectrum. The vertical and adiabatic electron affinities of HO2 (X2A″, A2A′) and electron photodetachment energies of HO2− (X1A′) to the X and A states of the neutral molecule are reported.

Rydberg, valence, and ion-pair quintet states of O2

We report an ab initio study of the quintet states of molecular oxygen. The calculations are carried out employing the multireference single and double excitation configuration interaction package. Potential energy curves of the six quintet valence states dissociating into ground state atoms and of the four quintet states dissociating to ion-pair atoms were computed. A number of bound quintet Rydberg series converging to the a(4)Πu and b(4)Σg(-) states of the O2(+) cation have been identified.

Franck–Condon factors using supervised artificial neural networks. I. The CF+ cation

Several studies of the electronic and vibrational structure of CF+ have been performed since this molecule was first discovered to occur in the interstellar medium, and even before that. However, researchers have paid little attention to calculating its Franck–Condon factors (FCFs), which can aid the identification of this molecule through comparison with the observed intensity spectrum. In this work, an analysis of all of the potential energy curves of CF+ that were candidates for this kind of calculation was undertaken. The Franck–Condon factors of CF+ were calculated using a supervised neural network with two layers and a variable learning rate.

Coupled-channel study of the Rydberg–valence interaction in HBr

We report an ab initio study of the low-lying valence and Rydberg states of HBr. The calculations are carried out employing the multireference single- and double-excitation configuration interaction method including the spin-orbit interaction. The first excited adiabatic potential of 1Σ+ symmetry presents two minima which correspond to the Rydberg E1Σ+ and valence V1Σ+ observed states. We calculate the vibrational levels of these two states using a coupled-channel treatment based on the two diabatic potentials deduced from the ab initio adiabatic potentials and the Rydberg-valence interaction. The chaotic energy separations between the observed levels are well reproduced in the calculations. We have also obtained for the first time theoretical data for numerous Rydberg states of HBr lying in the (66-79) × 103 cm-1 excitation energy interval. The calculated spectroscopic parameters are found to be in good agreement with experiment and provide a basis for future studies of radiative and non-radiative processes in the HBr molecule.