Fernando R. Ornellas

A theoretical investigation of the low‐lying electronic states of the molecule BeH+

A theoretical study at the multireference singles and doubles configuration‐interaction level is reported for the six lowest electronic states of BeH+. Of the four new states described, the 1Π and 3Π are bound states supporting at least 8 and 12 vibrational levels, respectively. Two 3Σ+ states are repulsive. For the two known 1Σ+ states improved results are also presented. For all these states, dipole moments and transition moments have been computed. For the bound states, besides the vibrational levels, transition probabilities, radiative lifetimes, vibrationally averaged dipole moments, and a set of spectroscopic constants are also reported.

A theoretical study of the electronic structure and spectroscopic properties of a new diatomic molecule, BeC

The 13 lowest‐lying electronic states of a new diatomic molecule, BeC, are described theoretically for the first time using the multireference single and double excitations configuration interaction approach. Potential energy curves are presented for all the states as well as a description of the electronic structure characterizing each of them. Dissociation and vertical excitation energies, and dipole moment functions complete the electronic structure description. Vibrational and rotational levels spacings, on the other hand, allowed the calculation of a whole set of spectroscopic constants characterizing each state. In its ground state, a 3Σ−, this molecule is more strongly bound (De=2.39 eV) than the recently described species BeN (De=1.34 eV) but still less strongly bound than BeO (De=4.69 eV) and BeF (De=5.82 eV). The first excited triplet state (3Π) shows an avoided crossing at short internuclear distances which should certainly reflect in perturbative effects in its spectrum. A distinctive feature ...

Theoretical characterization of hydrogen polyoxides: HOOH, HOOOH, HOOOOH, and HOOO.

We have investigated the polyoxides HOOH, HOOOH, HOOOOH, and HOOO employing the CCSD(T) methodology, and the correlation consistent basis sets. For all molecules, we have computed fundamental vibrational frequencies, structural parameters, rotational constants, and rotation-vibration corrections. For HOOOH, we have obtained a good agreement between our results and microwave and infrared spectra measurements, although for the symmetric OO stretch some important differences were found. Heats of formation were computed using atomization energies, and our recommendation is as follows: DeltaH(o)(f,298)(HOOOH) = -21.50 kcal/mol and DeltaH(o)(f,298)(HOOOOH) = -10.61 kcal/mol. In the case of HOOO, to estimate the heat of formation, we have constructed three isodesmic reactions to cancel high order correlation effects. The results obtained confirmed that the latter effects are very important for HOOO. The new DeltaH(o)(f,298)(HOOO) obtained is 5.5 kcal/mol. We have also calculated the zero-point energies of DO and DOOO to correct the experimental lower limit determined for the DeltaH(o)(f,298)(HOOO). The Delta(DeltaZPE) decreases the binding energy of HOOO by 0.56 kcal/mol. Employing the latter value, the new experimental lower limit for DeltaH(o)(f,298)(HOOO) is 3.07 kcal/mol, just 2.4 kcal/mol lower than our determination. We expect that the fundamental vibrational frequencies and rotational constants determined for HOOOOH and DOOOOD contribute to its identification in the gas phase. The vibrational spectrum of HOOOOH shows some overlapping with that of HOOOH thus indicating that one may encounter some difficulties in its characterization. We discuss the consequences of the thermochemical properties determined in this work, and suggest that the amount of HOOO present in the atmosphere is smaller than that proposed recently in this journal ( J. Phys. Chem A 2007, 111, 4727).

On the assignment of transitions involving some 2Π Rydberg states of the BeH molecule

Abstract Very accurate potential energy curves for several low-lying excited 2 Π states of the BeH molecule are reported using the multireference configuration approach. New features in the potential energy curves of the B and G  2 Π states not considered previously, like the existence of a double minimum, invalidate some of the arguments used in the assignment of transitions arising from these states. An alternative interpretation of some of the transitions and improved spectroscopic constants are presented. For the 3d states, for which experimental data are still uncertain about their nature, this study allows us to make an unambiguous correlation with the 3d 2 Π state.

Radiative transition probabilities, lifetimes, and dipole moments for all vibrational levels in the X 1Σ+ state of the beryllium hydride ion

The dipole moment function, vibrationally averaged dipole moment, radiative transition probabilities and radiative lifetimes are computed for all vibrational levels and selected rotational levels of the beryllium hydride molecule ion in the X 1Σ+ state.

A theoretical study of the molecules BeF and BeF+ in their lowest-lying electronic states

The two lowest-lying electronic states of the BeF molecule and the four lowest-lying electronic states of the ion BeF+ are described theoretically using the multi-reference single and double excitations configuration interaction approach. This description includes the calculation of potential energy curves, dissociation energies, vibrational energies, dipole and transition moment functions, averaged dipole moments, radiative transition probabilities and lifetimes and a whole set of spectroscopic constants. The quality of the results can be assessed, for example, from the computed vibrational spacings for which our values differ by no more than 9 cm-1 from the experimental data. Of the four states of BeF+, here described for the first time, the ground state shows a very deep well; the next two states are very weakly bound and the fourth state is a repulsive one.

Atmospheric reaction between the HS radical and chlorine

Abstract The mechanism and the kinetics of the reaction between HS and Cl2 leading to HSCl and Cl were studied theoretically. The effect of the complete basis set limit (CBS) was included by extrapolating the results obtained with cc-pVDZ, cc-pVTZ and cc-pVQZ correlation consistent basis sets functions. At the highest level of calculation, CCSD(T), the calculated rate constant is 1.0×10−12 cm3 molecule−1 s−1. The activation Gibbs free energy was calculated to be 7.4 kcal/mol, which is only 0.2 kcal/mol above the value determined experimentally. The enthalpy and Gibbs free energies of the reaction are −6.9 and −6.5 kcal/mol, respectively.

Plasmonic Nanorattles as Next-Generation Catalysts for Surface Plasmon Resonance-Mediated Oxidations Promoted by Activated Oxygen

Nanorattles, comprised of a nanosphere inside a nanoshell, were employed as the next generation of plasmonic catalysts for oxidations promoted by activated O2 . After investigating how the presence of a nanosphere inside a nanoshell affected the electric-field enhancements in the nanorattle relative to a nanoshell and a nanosphere, the SPR-mediated oxidation of p-aminothiophenol (PATP) functionalized at their surface was investigated to benchmark how these different electric-field intensities affected the performances of Au@AgAu nanorattles, AgAu nanoshells and Au nanoparticles having similar sizes. The high performance of the nanorattles enabled the visible-light driven synthesis of azobenzene from aniline under ambient conditions. As the nanorattles allow the formation of electromagnetic hot spots without relying on the uncontrolled aggregation of nanostructures, it enables their application as catalysts in liquid phase under mild conditions using visible light as the main energy input.

A theoretical description of the ion BeC+ and the photoelectron spectrum of BeC

Abstract The seven lowest-lying electronic states of the ion BeC + are described theoretically using the multi-reference single and double excitations configuration interaction approach. Potential energy curves are presented for all the states as well as a description of the electronic structure characterizing each of them. A whole set of spectroscopic constants completes the characterization of each state. In its ground states (…3δ1π 2 4δ, X 4 Σ − ) this molecule is more strongly bound ( D e =3.18 eV) than the neutral species ( D e = 2.39 eV) and consequently has a shorter equilibrium distance (2.960 a 0 ) compared to 3.150 a 0 of BeC. The first two excited states are a 2 Π ( R e = 3.420 a 0 ) and a 2 Δ ( R e = 2.973 a 0 ) at energies 0.528 and 1.582 eV. The first excited quartet ( 4 Π) lies at 1.971 eV ( R e = 3.616 a 0 ). Of the remaining doublets, the state d 2 Σ + is distinct for exhibiting a double minimum, with the inner equilibrium distance equal to 2.965 a 0 and the outer one equal to 3.681 a 0 ; a barrier of 0.25 eV at 3.263 a 0 separates the two wells. A combination of these results with those previously reported for the neutral species allowed the calculation of vertical and adiabatic ionization potentials and the prediction of photoelectron spectra based on the Franck-Condon distrubutions for transitions from the ground state of BeC to selected bound states of BeC + .

Radiative and predissociative lifetimes of the A 2Σ+ state (v′=0,1) of SH and SD: A highly correlated theoretical investigation

Doublet and quartet states of the HS radical correlating with H(2S)+S(3P,1D,1S) were investigated by ab initio calculations, at the CASSCF-MRCI/aug-cc-pV5Z level of theory. Molecular parameters and spectroscopic constants obtained for both the ground (X 2Π) and the first excited (A 2Σ+) states represent the best overall theoretical description of this system to date. Transition moments, transition probabilities, and radiative and predissociative lifetimes were also determined for the X 2Π–A 2Σ+ system. The values calculated for the radiative lifetimes of the A state show that previous results were too large. Theoretical predissociative lifetimes, although quite sensitive to the region of crossing of the potential energy curves, reproduce the experimental trends.