CAS SCF/CI calculations of potential energy surfaces of He3+ and He2+

Complete active space MC SCF (CAS SCF) calculations followed by second-order configuration interaction (SOCI) calculations are carried out on the potential energy surfaces (bending surface, linear surfaces) of the ²Σ_g⁺ ground state of He₃⁺. The potential minimum for the ²Σ_g⁺ state occurs at a linear geometry with HeHe bond length of 1.248 Å. The binding energy of He₃⁺ with respect to He + He⁺ + He was calculated to be 2.47 eV at the SOCI level. The energy required to dissociate He₃⁺ (²Σ_g⁺) into He₂⁺ (²Σ_u⁺) and He(¹S) is calculated to be 0.14 eV. The same level of SOCI calculations of He₂⁺ yield a D_e value of 2.36 eV.     

Ab initio MRD CI calculations for the electron spectrum of the C3 radical

Calculations using the MRD CI method are reported for the ground and low lying excited states of C₃. Transitions from the 3σ_u, 4σ_g and 1π_u MO's into 1π_g are considered, as well as the 1π_u → 3s Rydberg species and the corresponding ionization, and good agreement with experimental data is obtained where comparison is possible. Potential curves calculated for the ground and (1π_u → 1π_g) ¹Σ⁺_u excited state are discussed.     

Theoretical investigations on the SO2 + HO2 reaction and the SO2–HO2 radical complex

The mechanism of the SO₂ + HO₂ reaction was studied theoretically for the first time. Three product channels were revealed, namely, O₂ + HOSO, O₂ + HSO₂, and OH + SO₃. The O₂ + HOSO channel dominates the reaction under combustion conditions. A five-member-ring complex [SO₂–HO₂] exists at the entrance of the reaction. The structure and binding energy (D_e and D₀) of the SO₂–HO₂ complex have been calculated. In view of D₀ = 21.2 ± 2.0 kJ mol⁻¹, the SO₂–HO₂ complex should be stable at low temperature. The infrared spectra and frequency shifts were calculated for both SO₂–HO₂ and SO₂–DO₂, and compared with the available experimental data.     

Quantum Dynamics of Oxyhydrogen Complex-Forming Reactions for the HO2 and HO3 Systems

Complex-forming reactions widely exist in gas-phase chemical reactions.Various complexforming bimolecular reactions have been investigated and interesting phenomena have been discovered.The complex-forming reactions usually have small or no barrier in the entrance channel, which leads to obvious differences in kinetic and dynamic characteristics compared with direct reactions.Theoretically, quantum state-resolved reaction dynamics can provide the most detailed microscopic dynamic mechanisms and is now feasible for a direct reaction with only one potential barrier.However, it is of great challenge to construct accurate potential energy surfaces and perform accurate quantum dynamics calculations for a complex polyatomic reaction involving deep potential wells and multi-channels.This paper reviews the most recent progress in two prototypical oxyhydrogen complex-forming reaction systems, HO₂ and HO₃, which are significant in combustion, atmospheric, and interstellar chemistry.We will present a brief survey of both computational and experimental work and emphasize on some unsolved problems existing in these systems.     

The temperature dependence of the HO2 + HO2 reaction

The temperature dependence of the rate constant for the reaction HO₂ + HO₂ → H₂O₂ + O₂ (2k₁) has been determined using flash photolysis techniques, over the temperature range 298–510 K, in a nitrogen diluent at a total pressure of 700 Torr. The overall second order state constant is given by k₁ = (4.14 ± 1.15) × 10^?13 exp[(630 ± 115)/T] cm³ molecule^?1 s^?1, where the quoted errors refer to one standard deviation. This result is compared with previous findings and the negative activation energy is shown to be consistent with the observation that the rate constant is pressure dependent at 700 Torr.     

CAS SCF calculations of potential enregy curves for the BO− ion

The oxoborate ion BO^? has been investigated at the MC SCF level of approximation, using an augmented double-zeta basis. Potential curves have been calculated for the three lowest states. The results are compared to those obtained for BO in a previous, similar study.     

Non-empirical SCF and CI study of the SOH radical

The build-up of triplet—triplet absorption was measured for acridine and phenazine in the gas phase by the picosecond spectroscopy method, and we obt     

Ci calculations of the low lying electronic states of the radical SiH3, SiH+3 and SiH−3

SCF and CI calculations for the silicon-hydrogen compounds SiH₃, SiH⁺₃ and SiH^? with D_3h and C_3v geometries are carried out f     

CAS SCF Cl calculations for the 3Σ−g, 1Σ+g, 3Σ+u, and 5Δu states of Sc2

CAS SCF CI (SD) calculations have been carried out for the ³Σ^?_g, ¹Σ⁺_g, ³Σ⁺_u, and ⁵Δ_u states of Sc₂ using large gaussian basis sets. The ³Σ^?_g, ¹Σ⁺_g, and ³Σ⁺_u states arise from the ²D(4s² 3d¹) + ²D(4s² 3d¹) limit of Sc₂ and are found to be only weakly bound (D_c ≈ 0.06 eV and R_c ≈ 8.0a₀). The ⁵Δ_u state arises from the ²D(4s² 3d¹) + ⁴F(4s¹ 3d¹ 4p¹) atomic limit. This state is found to be strongly bound relative to its limits (D_c ≈ 0.8 eV and R_c ≈ 7.0a₀).     

Correlation effects on hydrogen-bond potentials. SCF Cl calculations for the systems HF−2 and H3O−2

The effects of neglecting electron correlation in the Hartree-Fock approximation have been investigated for selected properties of two strongly hydrogen-bonded systems. Accounting for correlation will substantially lower and, in some cases, remove barriers for proton transfer which have been obtained using the Hartree-Fock approximation. As a consequence, the asymmetric hydrogen-bond stretching frequencies in HF^?₂ are found to increase when correlation is included in the calculations, contrary to the case for more regular stretching frequencies. The hydrogen-bond energies of the two systems are found to be rather insensitive to correlation effects.     

An SCF and CI study of the properties of the HCl and CI2 molecules

The one-electron properties and polarizabilities of the HCl and Cl₂ molecules have been calculated using both SCF and CI wavefunctions. Agreement with experimental data, where such data exist, is found to be very good.     

Ground-state dipole polarizability of lithium hydride. Accurate SCF and CAS SCF calculations

Accurate calculations of the dipole polarizability tensor of lithium hydride are performed using the finite-field perturbation approach in the SCF and CAS SCF method. The SCF results (α_? = 22.1, α_⊥ = 25.4 au) are expected to be very close to the HF values. The CAS SCF calculations predict a positive correlation contribution, giving α_? = 26.3 and α_⊥ = 29.3 au.     

Reactions of HO2 with NO,OH and HO2 studied by EPR/LMR spectroscopy

A combined EPR/LMR spectrometer and fast-flow system has been used to investigate the reactions HO₂ + NO(k₁), HO₂ + OH(k₂), HO₂ + HO₂(k₃) at room temperature. The rate constants have been measured: k₁ = (7.0 ± 0.6) × 10^?12 cm³ s^?1 (P = 7–10 Torr);k₂ = (5.2 ± 1.2) × 10^?11 cm³ s^?1 (P = 8–10 Torr);k₃ = (1.65 ± 0.3) × 10^?12 cm³ s^?1 (P = 2.1–24.9 Torr). The conclusion is drawn from analysis of the literature and the present work that k₂ and k₃ do not depend on pressure up to 1 atm.     

Valence and core ionization energies for SiH4, H3SiCl and H3CCl from SCF and PNO-CEPA calculations

Valence and core ionization energies for the molecules SiH₄, H₃SiCl and H₃CCl have been obtained from RHF-SCF and PNO-CEPA wavefunctions. The calculated vertical ionization energies IE_n^v(n = 1, 2, 3) agree within about 0.2 eV with the PE spectroscopically determined values for SiH₄, H₃SiCl and H₃CCl. The increase in IE₁^v for H₃SiCl relative to H₃CCl, which has been previously ascribed to a different d-orbital participation in the two molecules, is already reproduced by calculations with (s, p) basis sets. The ΔSCF method has been used to predict several core ionization energies. In addition, relative intensities calculated for the ionizations into the ²A₁ states of SiH₄⁶ are compared with available experimental data, and some spectroscopic constants for SiH₄ and its ionic states are predicted.     

SCF MO CI calculations on the electronic spectra of fluorenone and related compounds

The electronic spectra of fluorenone, 9-iminofluorene and 9-ethylidenefluorene are studied by means of the SCF MO CI calculation. It is shown that the lowest singlet-singlet transition of fluorenone located at 380 m. can be assigned to a - ^* transition (¹ B ₂¹ A ₁). The nature and location of the lowest triplet state are also discussed.

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Zusammenfassung Die Elektronenspektren von Fluorenon, 9-Iminofluoren und 9-Äthylidenfluoren werden mit Hilfe der SCF MO CI-Methode studiert. Es wird gezeigt, daß der niedrigste Sigulett-Singulett-Übergang in Fluorenon bei 380 m einem ^*-Übergang (¹ B ₂¹ A ₁) zugeordnet werden kann. Die Natur und Lage des niedrigsten Triplett-Übergangs werden ebenfalls studiert.

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Résumé Les spectres électroniques de la fluorenone, du 9 iminofluorène et du 9-éthylidène fluorène sont étudiés à l'aide de calculs SCF-MO-CI. On montre que la plus basse transition singuletsingulet de la fluorénone, située à 380 m, peut être attribuée à une transition ^* (¹ B ₂¹ A ₁ La nature et la position du plus bas état triplet sont aussi étudiées.