Core-valence Correlation Corrections Research Articles

Accurate thermochemistry at affordable cost by means of an improved version of the JunChS-F12 model chemistry.

The junChS-F12 composite method has been improved by means of the latest implementation of the CCSD(F12*)(T+) ansatz and validated for the thermochemistry of molecules containing atoms of the first three rows of the periodic table. A thorough benchmark showed that this model, in conjunction with cost-effective revDSD-PBEP86-D3(BJ) reference geometries, offers an optimal compromise between accuracy and computational cost. If improved geometries are sought, the most effective option is to add MP2-F12 core-valence correlation corrections to CCSD(T)-F12b/jun-cc-pVTZ geometries without the need of performing any extrapolation to the complete basis set limit. In the same vein, CCSD(T)-F12b/jun-cc-pVTZ harmonic frequencies are remarkably accurate without any additional contribution. Pilot applications to noncovalent intermolecular interactions, conformational landscapes, and tautomeric equilibria confirm the effectiveness and reliability of the model.

A theoretical study on the electronically excited-state spectroscopic properties of phosphorus nitride

ABSTRACT The potential energy curves of 103 Ω states generated from the 39 Λ–S states of PN have been calculated using the internally contracted multireference configuration interaction method with the Davidson modification. Core-valence correlation and scalar relativistic corrections, as well as the basis-set extrapolation to the complete basis set limit are considered. The spin–orbit coupling is computed using the state interaction approach with the Breit-Pauli Hamiltonian. The spectroscopic parameters and molecular constants of bound and quasibound Λ–S and Ω states are evaluated. Our calculated spectroscopic results agree quite well with the available experimental data. The interactions among different electronic states in curve crossing regions have been discussed with the help of computed spin–orbit coupling matrix elements. The perturbations and predissociation phenomena of the A1 , b3 , D1Δ, E1Σ+, and 21 states and so on have been revealed.

JunChS and junChS-F12 Models: Parameter-free Efficient yet Accurate Composite Schemes for Energies and Structures of Noncovalent Complexes.

A recently developed model chemistry (denoted as junChS [Alessandrini, S.; et al. J. Chem. Theory Comput. 2020, 16, 988-1006]) has been extended to the employment of explicitly correlated (F12) methods. This led us to propose a family of effective, reliable, and parameter-free schemes for the computation of accurate interaction energies of molecular complexes ruled by noncovalent interactions. A thorough benchmark based on a wide range of interactions showed that the so-called junChS-F12 model, which employs cost-effective revDSD-PBEP86-D3(BJ) reference geometries, has an improved performance with respect to its conventional counterpart and outperforms well-known model chemistries. Without employing any empirical parameter and at an affordable computational cost, junChS-F12 reaches subchemical accuracy. Accurate characterizations of molecular complexes are usually limited to energetics. To take a step forward, the conventional and F12 composite schemes developed for interaction energies have been extended to structural determinations. A benchmark study demonstrated that the most effective option is to add MP2-F12 core-valence correlation corrections to fc-CCSD(T)-F12/jun-cc-pVTZ geometries without the need of recovering the basis set superposition error and the extrapolation to the complete basis set.

Transition properties of a2Σ–, b2Δ, c2Π, d2Π, and e2Σ+ electronic states of aluminum silicon radical

Detecting aluminum silicon can yield useful information concerning the depletion of silicon and aluminum and their recycling in astrophysical sources. In addition, such detection can be helpful for understanding gas–phase aluminum and silicon chemistry in the interstellar/circumstellar atmosphere. However, only a few transition properties of this radical have been reported. Therefore, the potential energy curves of several lowest–lying doublet states and the transition dipole moments between them were calculated using the icMRCI approach. Core–valence correlation correction, scalar relativistic correction, and spin–orbit coupling effect were included to improve the accuracy of transition properties. The radiative lifetimes of the first 16 levels were approximately 4.8 – 679.5 ms for the c2Π1/2 state, 2.2 – 431 ms for the c2Π3/2 state, 29.3 – 40.4 µs for the d2Π1/2 state, 21.2 – 30.1 µs for the d2Π3/2 state, and 88.7 – 175.6 µs for the e2Σ+1/2 state. The spontaneous emissions from the c2Π1/2 and c2Π3/2 states to the a2Σ–1/2, b2Δ3/2, and b2Δ5/2 states and those from the e2Σ+1/2 state to the d2Π1/2 and d2Π3/2 states were located in the radio–frequency region. The d2Π1/2 – a2Σ–1/2 and d2Π3/2 – a2Σ–1/2 transitions were the strongest, followed by d2Π1/2 – b2Δ3/2, d2Π3/2 – b2Δ3/2, d2Π3/2 – b2Δ5/2, d2Π1/2 – c2Π1/2, d2Π3/2 – c2Π3/2, e2Σ+1/2 – c2Π1/2, and e2Σ+1/2 – c2Π3/2 transitions. The spontaneous emissions from these systems were located in the infrared region. The variation in the radiative lifetime of a level υ versus the rotational quantum number J was investigated for the d2Π1/2, d2Π3/2, and e2Σ+1/2 states.

Theoretical Investigation on the Laser Cooling of AlD Molecule

The potential energy curves for four Λ-S and eight Ω states of the AlD molecule are calculated by using the valence internally contracted multireference configuration interaction approach with the Davidson modification (icMRCI+Q). The core-valence correlation and relativistic corrections are included. The extrapolation of potential energies to the complete basis set limit is made. Transition dipole moments (TDMs) between the six bound Ω states are also calculated by the icMRCI approach. The calculated spectroscopic constants are in good agreement with the available experimental data and theoretical values. Based on the obtained potential energy curves and transition dipole moments, highly diagonal Franck-Condon factors and vibrational branching ratios are determined for the A1π1(υ'=0,1)→X1Σ+0+(υ'') transition, short spontaneous radiative lifetime and narrow radiative width for the excited state A1π1 (υ'=0, 1) are also predicted. On this account, the optical scheme of the laser cooling for AlD molecule is constructed with A1π1(υ')↔X1Σ+0+(υ'') as the close-loop transition. The proposed laser drives X1Σ+0+(υ'')→A1π1(υ') transition by using three wavelengths (main laser beam λ00=420.96 nm; two repumping laser beams λ10=443.00 nm and λ21=448.94 nm). The Doppler temperature (TDoppler=44.94 μK) and recoiltemperature(TRecoil=3.73 μK) for the A1π1 (υ'=0)X1Σ+0+ (υ''=0) transition are also calculated. These results can provide theoretical support for the experimental study of laser-cooled AlD molecules.

Rovibrational transition properties of the X1Σ+ and A1Π states of carbon monosulfide

Carbon monosulfide was detected in outer space by rovibrational spectroscopy of the X 1Σ+ state and A 1Π – X 1Σ+ system. This work calculated the potential energy curves and dipole moment functions of the X 1Σ+ 0+ and A 1Π1 states, and computed the transition dipole moments between the two states employing the CASSCF method, followed by the valence icMRCI approach. Core-valence correlation and scalar relativistic corrections were included. The extrapolation of potential energies to the complete basis set limit was performed. The spin-orbit coupling effect was included. The Einstein A coefficients, band origins, and oscillator strengths were calculated for the rovibrational transitions when J ≤ 150. The rovibrational transitions of the X 1Σ+ 0+ and A 1Π1 states became very weak when Δυ ≥ 6. The Einstein A coefficients of vibronic emissions of the A 1Π1 – X 1Σ+ 0+ system were large, indicating that the emissions were able to be measured easily through spectroscopy. Several rovibrational transitions of the A 1Π1 – X 1Σ+ 0+ system were analysed in detail. The distribution of radiative lifetime varying as rotational quantum number was calculated. The results obtained in this work agree well with the available experimental values.

Molecular opacities of low-lying states of oxygen molecule**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0402300), the National Natural Science Foundation of China (Grant Nos. 11934004, 11404180, and 11604052), and the China Postdoctoral Science Foundation (Grant No. 2018M631404).

The , A′3Δu, , 13Πg, and electronic states of oxygen molecule (O2) are calculated by the multi-configuration self-consisted filed (MRCI) + Q method with the scalar relativistic correction and core–valence correlation correction. The obtained spectroscopic constants of the low-lying bound states are in excellent agreement with measurements. Based on the accurately calculated structure parameters, the opacities of the oxygen molecule at the temperatures of 1000 K, 2000 K, 2500 K, and 5000 K under a pressure of 100 atm (1 atm = 1.01325 × 105 Pa) and the partition functions between 10 K and 104 K are obtained. It is found that with the increase of temperature, the opacities for transitions in a long wavelength range are enlarged because of the larger population on excited electronic states at the higher temperatures.

High-Level Ab Initio Predictions for the Ionization Energy, Bond Dissociation Energies, and Heats of Formation of Vanadium Methylidyne Radical and Its Cation (VCH/VCH+).

The ionization energy (IE) of VCH, the 0 K V-CH/VC-H bond dissociation energies (D0s), and the heats of formation at 0 K (ΔHf0°) and 298 K (ΔHf298°) for VCH/VCH+ are predicted by the wave function-based CCSDTQ/CBS approach. This composite-coupled cluster method includes full quadruple excitations in conjunction with the approximation to the complete basis set (CBS) limit. The contributions of zero-point vibrational energy, core-valence (CV) correlation, spin-orbit coupling, and scalar relativistic corrections are taken into account. The present calculations show that adiabatic IE(VCH) = 6.785 eV and demonstrate excellent agreement with an IE value of 6.774 7 ± 0.000 1 eV measured with two-color laser-pulsed field ionization-photoelectron spectroscopy. The CCSDT and MRCI+Q methods which include CV correlations give the best predictions of harmonic frequencies: ω2 (ω2+) (bending) = 534 (650) and 564 (641) cm-1 and the V-CH stretching ω3 (ω3+) = 835 (827) and 856 (857) cm-1 compared with the experimental values. In this work, we offer a streamlined CCSDTQ/CBS approach which shows an error limit (≤20 meV) matching with previous benchmarking efforts for reliable IE and D0 predictions for VCH/VCH+. The CCSDTQ/CBS D0(V+-CH) - D0(V-CH) = -0.012 eV and D0(VC+-H) - D0(VC-H) = 0.345 eV are in good accord with the experimentally derived values of -0.028 4 ± 0.000 1 and 0.355 9 ± 0.000 1 eV, respectively. The present study has demonstrated that the CCSDTQ/CBS protocol can be readily extended to investigate triatomic molecules containing 3d-metals.

Spectroscopic properties and transition probabilities of SiC+ cation

This study calculates the potential energy curves of 12 Λ-S and 27 Ω states, which belong to the first dissociation channel of SiC+ cation. The potential energy curves are computed with the complete active space self–consistent field method, which is followed by the valence internally multireference configuration interaction approach with the Davidson correction. The transition dipole moments are determined. Core-valence correlation and scalar relativistic correction, as well as extrapolation of the potential energies to the complete basis set limit are included. The spin-orbit coupling effect on the spectroscopic parameters and vibrational properties is evaluated. The vibrational band origins, Franck–Condon factors, and Einstein coefficients of spontaneous emissions are calculated. The rotationless radiative lifetimes of the vibrational levels are approximately 10−5 s long for the e2Π state. The partial radiative lifetimes of vibrational levels are approximately 10−7 s long for the 24Π and 24Σ− states, 10−5 to 10−6 s long for the 22Σ− state and the first well of the 14Π state, and very short for the second well of the 14Π state. Overall, the emissions are strong for the 22Σ−–c2Σ−, 24Σ−–X4Σ−, 24Π–X4Σ− transitions, and for the second well of the 14Π–14Σ+ transition. The spectral range of emissions is determined. In terms of the radiative lifetimes and transition probabilities obtained in this paper, some guidelines for detecting these states are proposed via spectroscopy. These results can be used to measure the emissions from the SiC+ cation, in particular, in interstellar clouds.

MRCI study on transition dipole moments and transition probabilities of 18 low-lying states of CP+ cation

This study calculates the potential energy curves of 18 Λ-S and 50 Ω states, which arise from the C(3Pg) + P+(3Pg) dissociation channel of the CP+ cation. The calculations are made using the CASSCF method, followed by the icMRCI approach with the Davidson correction. Core-valence correlation and scalar relativistic corrections, as well as extrapolation to the complete basis set limit are included. The transition dipole moments are computed for 25 pairs of Λ-S states. The spin–orbit coupling effect on the spectroscopic and vibrational properties is evaluated. The Franck–Condon factors and Einstein coefficients of emissions are calculated. Radiative lifetimes are obtained for several vibrational levels of some states. The transitions are evaluated and spectroscopic measurement schemes for observing these Λ-S states are proposed. The potential energy curves, spectroscopic constants, vibrational levels, transition dipole moments, and transition probabilities reported in this paper can be considered to be very accurate and reliable. Because no experimental observations are currently available, the results obtained here can be used as guidelines for the detection of these states in appropriate spectroscopy experiments, in particular for observations in stellar atmospheres and in interstellar space.

Rotational and Infrared Spectroscopy of Ethanimine: A Route toward Its Astrophysical and Planetary Detection

Abstract Ethanimine, a possible precursor of amino acids, is considered an important prebiotic molecule and thus may play important roles in the formation of biological building blocks in the interstellar medium. In addition, its identification in Titan’s atmosphere would be important for understanding the abiotic synthesis of organic species. An accurate computational characterization of the molecular structure, energetics, and spectroscopic properties of the E and Z isomers of ethanimine, CH3CHNH, has been carried out by means of a composite scheme based on coupled-cluster techniques, which also account for extrapolation to the complete basis-set limit and core-valence correlation correction, combined with density functional theory for the treatment of vibrational anharmonic effects. By combining the computational results with new millimeter-wave measurements up to 300 GHz, the rotational spectrum of both isomers can be accurately predicted up to 500 GHz. Furthermore, our computations allowed us to revise the infrared spectrum of both E- and Z-CH3CHNH, thus predicting all fundamental bands with high accuracy.

IcMRCI+Q Study of the Spectroscopic Properties of the 14 Λ-S and 49 Ω States of the SiN- Anion in the Gas Phase.

This paper calculates the potential energy curves of the 14 Λ-S and 49 Ω states, which come from the first three dissociation channels of the SiN− anion. These calculations are conducted using the valence internally contracted multireference configuration interaction and the Davidson correction approach. Core-valence correlation and scalar relativistic corrections are taken into account. The potential energies are extrapolated to the complete basis set limit. The spin-orbit coupling is computed using the state interaction approach with the Breit–Pauli Hamiltonian. We found that the X1Σ+ (υ′′ = 0–23) and a3Σ+ (υ′ = 0–2) states of SiN− are stable at the computed adiabatic electron affinity value of 23,262.27 cm−1 for SiN. Based on the calculated potential energy curves, the spectroscopic parameters and vibrational levels were determined for all stable and metastable Λ-S and Ω states. The computed adiabatic electron affinity of SiN and the spectroscopic constants of SiN− (X1Σ+) are all in agreement with the available experimental data. The d3Σ+, 25Σ+, 15Δ, and 15Σ− quasi-bound states caused by avoided crossings were found. Calculations of the transition dipole moment of a3Σ+1 to X1Σ+0+ are shown. Franck-Condon factors, Einstein coefficients, and radiative lifetimes of the transition from the a3Σ+1 (υ′ = 0–2) to the X1Σ+0+ state are evaluated.

MRCI study on the spectroscopic parameters, transition dipole moments and transition probabilities of 16 low-lying states of the BeB radical

In this work, we calculate the potential energy curves of 16 Λ-S and 36 Ω states of beryllium boride (BeB) radical using the complete active space self-consistent field method, followed by the valence internally contracted multireference configuration interaction approach with Davidson correction. The 16 Λ-S states are the X2Π, A2Σ+, B2Π, C2Δ, D2Ʃ−, E2Σ+, G2Π, I2Σ+, a4Σ−, b4Π, c4Σ−, d4Δ, e4Σ+, g4Π, h4Π, and 24Σ+, which are obtained from the first three dissociation channels of the BeB radical. The Ω states are obtained from the Λ-S states. Of the Λ-S states, the G2Π, I2Σ+, and h4Π states exhibit double well curves. The G2Π, b4Π, and g4Π states are inverted with the spin-orbit coupling effect included. The d4Δ, e4Σ+, and g4Π states as well as the second well of the h4Π state are very weakly bound. Avoided crossings exist between the G2Π and H2Π states, the A2Σ+ and E2Σ+ states, the c4Σ− and f4Σ− states, the g4Π and h4Π states, the I2Σ+ and 42Σ+ states, as well as the 24Σ+ and 34Σ+ states. To improve the quality of the potential energy curves, core-valence correlation and scalar relativistic corrections, as well as the extrapolation of the potential energies to the complete basis set limit, are included. The transition dipole moments are computed. Spectroscopic parameters and vibrational levels are determined along with Franck–Condon factors, Einstein coefficients, and radiative lifetimes of many electronic transitions. The transition probabilities are evaluated. The spin-orbit coupling effect on the spectroscopic parameters and vibrational levels is discussed. The spectroscopic parameters, vibrational levels, and transition probabilities reported in this paper can be considered very reliable and can be employed to predict these states in an appropriate spectroscopy experiment.

Rovibrational spectrum calculations of four electronic states in carbon monoxide molecule: Comparison of two effect correction methods

Accurate calculation of molecular energy is of great significance for studying molecular spectral properties. In this work, the potential energy curve and rovibrational spectrum (Gν) of the ground state X1∑+ and the excited states a3Π, a'3∑+ and A1Π of carbon monoxide molecule are calculated by the multi-reference configuration interaction method. In the calculation, the core-valence correlation correction (CV) effect and scalar relativistic (SR) effect are included.In order to obtain an accurate energy of molecule, two computational schemes are adopted. In the first scheme, i.e. (m MRCI+Q/CBS(TQ5)+CV+SR), the molecular orbital wavefunction is obtained from the Hartree-Fock self-consistent field method by using the basis set aug-cc-pVnZ. The wavefunction is first calculated by the state-averaged complete active space self-consistent field approach. Then the multi-reference configuration interaction method (MRCI) is adopted to calculate the dynamic correlation energy in the potential energy curve. Finally, we use the basis set cc-pCVQZ and aug-cc-pVQZ to calculate the CV effect and SR effect by the MRCI method. In the second scheme (aug-cc-pwCVnZ-DK (n=T, Q, 5)), the potential energy curves (PECs) of these four electronic states are calculated by the MRCI method whose basis set (aug-cc-pwCVnZ-DK) contains the CV effect and SR effect. Finally, in order to reduce the error caused by the basis set, we extrapolate the basis sets of the two computational schemes to the complete basis set. On the basis of the PECs plotted by the different methods, we obtain the spectroscopic parameters of the X1∑+, a3Π, a'3∑+ and A1Π states of the carbon monoxide by solving the internuclear Schrödinger equations through utilizing the numerical integration program “LEVEL”.In this paper, we calculate the SR effect and the CV effect by using different schemes, and the latter is indispensable for accurately calculating the molecular structure. For the lowest two electronic states, we consider the dependence of the two effects on the calculation of the Gaussian basis group (Method B), and find that the accuracy of the rovibrational spectrum is improved. It can be seen that these electronic states have higher requirements for electronic correlation calculation. For higher electronic states, the electron cloud distribution is relatively loose, and the electronic correlation obtained by a single Gaussian basis group can achieve the corresponding calculation accuracy. Of course, since the calculation of the rovibrational spectra is essentially only the relative energy, the offset effect of the electronic correlation effect of different electronic states is also included here in this paper.

IcMRCI+Q study on spectroscopic properties and predissociation mechanisms of electronic states of BF+ cation

In this paper, we study the spectroscopic properties and predissociation mechanisms of 14 states, which come from the first two dissociation channels of the BF+ cation. The potential energy curves of 14 Λ-S (X2Σ+, 12Π, 22Π, 22Σ+, 14Σ+, 14Δ, 14Σ1, 12Δ, 12Σ1, 32Σ+, 14Π, 24Π, 24Σ+, and 32Π) and corresponding 30 Ω states are calculated using the complete active space self-consistent field method, which is followed by the valence internally contracted multireference configuration interaction approach with the Davidson modification. To improve the reliability and accuracy of the potential energy curves, the core-valence correlation and scalar relativistic corrections, as well as the extrapolation of potential energy to the complete basis set limit are taken into account. The spin-orbit coupling is computed using the state interaction approach with the Breit-Pauli Hamiltonian. Based on these potential energy curves, the spectroscopic parameters and vibrational levels are determined for all the bound and quasi-bound Λ-S and Ω states. The present ground-state spectroscopic constants match well with the available experimental data. In addition, the vertical and adiabatic ionization potentials from the X1Σ+ state of BF molecule to the X2Σ+, 12Π, and 22Σ+ states of BF+ cation are calculated. The results of BF+(X2Σ+) ← BF(X1Σ+) ionization are in good agreement with the measurements. Various curve crossings of Λ-S states are revealed. We calculate the spin-orbit matrix elements between two interacting electronic states in the curve crossing region. With the help of present spin-orbit coupling matrix elements, we analyze the predissociation mechanisms of X2Σ+ and 32Π states along with the perturbations of the nearby states to 22Π, 14Σ+ and 32Σ+ states for the first time. The predissociation of X2Σ+ and 32Π states have a chance to occur around the vibrational levels υ"=30 and υ'=0 due to spin-orbit coupling, respectively. The present results also indicate that the υ' ≥ 9 vibrational levels of 22Π state are perturbed by the crossing states 22Σ+, 14Σ+, 14Δ, 14Σ1, 12Δ, 12Σ1, 32Σ+, and 14Π, that the υ' ≥ 4 vibrational levels of 14Σ+ state are perturbed via the interacting states 14Σ1 and 12Σ1, and the great perturbations between υ' ≥ 4 vibrational levels of 32Σ+ state and υ' ≥ 0 vibrational levels of 14Π state. For the 30 Ω state, we also calculate the relative energies of dissociation limits compared with the lowest one matching well with the experimental ones. Finally, the Franck-Condon factors, Einstein coefficients, and radiative lifetimes are evaluated for the 22Π (υ'=0-9)-X2Σ+, 22Σ+ (υ'=0-2)-X2Σ+, (3)1/2-(1)1/21st well, and (2)3/2 (υ'=0-9)-(1)1/21st well transitions.

Theoretical study of spectroscopic properties of 5 -S and 10 states and laser cooling for AlH+ cation

In this paper, we calculate the potential energy curves of 5 -S and 10 , which arise from the first two dissociation limits of the AlH+ cation. The calculations are done using the complete active space self-consistent field method, which combines with the valence internally contracted multireference configuration interaction plus the Davidson modification (icMRCI+Q) approach with the aug-cc-pV6Z basis set. To improve the reliability and accuracy of the potential energy curves, the core-valence correlation and scalar relativistic correction, as well as the extrapolation of potential energy to the complete basis set limit are taken into account. The spin-orbit coupling is computed using the state interaction approach with the Breit-Pauli Hamiltonian. Employing the potential energy curves obtained in this study, we evaluate the spectroscopic parameters and vibrational levels for the bound and quasi-bound 4 -S and 8 states. The computed spectroscopic constants of X2+ and A2 states are all in agreement with the available experimental data. Moreover, the present theoretical energy separations between each higher channel (Al+(3P0) + H(2S1/2), Al+(3P1) + H(2S1/2), and Al+(3P2) + H(2S1/2) and the lowest one (Al+(1S0) + H(2S1/2)) are in excellent agreement with the experimental values. The transition dipole moments are calculated using the valence internally contracted multireference configuration interaction approach with the aug-cc-pV6Z basis set for the 2(1/2) X21/2+ and A23/2X21/2+. Based on the obtained potential energy curves and transition dipole moments, highly diagonally distributed Franck-Condon factors (f00 and f11) and large vibrational branching ratios are determined for the 2(1/2)1st well (v'=0, 1) X21/2+ (v) and A23/2(v'=0,1)X21/2+(v) transitions; short spontaneous radiative lifetime and narrow radiative width for the 2(1/2)1st well (v'=0, 1) and A23/2 (v'=0, 1) are also predicted in this study, which are suitable for the rapid laser cooling of the AlH+ cation. The three required laser cooling wavelengths are all in the ultraviolet region, that is, 1) for the X21/2+(v) 2(1/2)1st well (v') transition:the main repumping laser 00=358.74 nm, two repumping lasers 10=379.27 nm and 21=374.86 nm; 2) for the X21/2+ (v) A23/2 (v') transition:the main repumping laser 00=357.43 nm, two repumping lasers 10=377.80 nm and 21=373.26 nm. In addition, the recoil temperature for the X21/2+ (v=0) 2(1/2)1st well (v'=0) and X21/2+ (v=0) A23/2 (v'=0) transitions are obtained. The results imply the feasibility of laser cooling of AlH+ cation. In addition, the spin-orbit coupling effect on the spectroscopic parameter, vibrational level, and laser cooling of AlH+ cation are evaluated.

Spectroscopic parameters, vibrational levels, transition dipole moments and transition probabilities of the 9 low-lying states of the NCl+ cation

This work calculates the potential energy curves of 9 Λ-S and 28Ω states of the NCl+ cation. The technique employed is the complete active space self-consistent field method, which is followed by the internally contracted multireference configuration interaction approach with the Davidson correction. The Λ-S states are X2Π, 12Σ+, 14Π, 14Σ+, 14Σ−, 24Π, 14Δ, 16Σ+, and 16Π, which are yielded from the first two dissociation channels of NCl+ cation. The Ω states are generated from these Λ-S states. The 14Π, 14Δ, 16Σ+, and 16Π states are inverted with the spin-orbit coupling effect included. The 14Σ+, 16Σ+, and 16Π states are very weakly bound, whose well depths are only several-hundredcm−1. One avoided crossing of PECs occurs between the 12Σ+ and 22Σ+ states. To improve the quality of potential energy curves, core-valence correlation and scalar relativistic corrections are included. The potential energies are extrapolated to the complete basis set limit. The spectroscopic parameters and vibrational levels are calculated. The transition dipole moments are computed. The Franck-Condon factors, Einstein coefficients, and radiative lifetimes of many transitions are determined. The spectroscopic approaches are proposed for observing these states according to the transition probabilities. The spin-orbit coupling effect on the spectroscopic and vibrational properties is evaluated. The spectroscopic parameters, vibrational levels, transition dipole moments, as well as transition probabilities reported in this paper could be considered to be very reliable.

Study on the spectroscopic parameters and transition probabilities of 25 low-lying states of the AlC+ cation

This paper investigates the spectroscopic parameters and transition probabilities of 25 low-lying states, which come from the first five dissociation channels of AlC+ cation. The potential energy curves are calculated with the complete active space self-consistent field method, which is followed by the valence internally contracted multireference configuration interaction approach with Davidson correction. Of these 25 states, only the 35Σ−state is repulsive; the c1Σ+, f1Π, and 15Π states have the double well; the first well of c1Σ+ state and the second well of 15Π state are very weakly bound; the first well of c1Σ+ state has no vibrational levels; the 25Π state and the double well of f1Π state have only several vibrational states; the B3Σ−, E3Σ+, D3Π, 15Σ+, 25Σ−, and 15Π states are inverted when the spin-orbit coupling effect is included. The avoided crossings exist between the B3Σ− and 33Σ− states, the c1Σ+ and d1Σ+ states, the f1Π and 31Π states, the 15Π and 25Π states, as well as the 25Π and 35Π states. Core-valence correlation and scalar relativistic corrections are considered. The extrapolation of potential energies to the complete basis set limit is done. The spectroscopic parameters and vibrational levels are determined for all the Λ–S and Ω bound states. The transition dipole moments are calculated. Franck–Condon factors of a great number of electronic transitions are evaluated. On the whole, the spin-orbit coupling effect on the spectroscopic parameters and vibrational levels is small except for very few states. The results determined in this paper could provide some powerful guidelines to observe these states in a spectroscopy experiment.

MRCI study of the spectroscopic parameters and transition properties of the 36 low-lying electronic states of the B2 molecule

This paper studied the spectroscopic and transition properties of 36 low-lying states, which came from the first two dissociation limits of B2 molecule. The potential energy curves were calculated with the complete active space self-consistent field (CASSCF) method, which was followed by the internally contracted multireference configuration interaction (icMRCI) plus Davidson modification (icMRCI+Q) approach. Of these 36 states, the 25Σu−, 15Σu+, 25Πu, and 15Δu states were repulsive; the B3Δu, E3Σu+, f1Σu−, g1Πg, 23Πu, 33Σg−, 33Πu, 15Πg, and 33Σu+ states had double wells; the B3Δu, E3Σu+, G3Σu+, f1Σu−, g1Πg, 33Σg−, 23Πu, 33Πu, 15Πg, 25Πg, 25Σg−, and 33Σu+ states had one barrier; the 25Σg− state and the second wells of B3Δu, E3Σu+, 15Πg, f1Σu−, g1Πg, and 23Πu states were weakly bound; and the 25Σg− state had no vibrational levels. The avoided crossings existed between the B3Δu and 23Δu states, the E3Σu+ and G3Σu+ states, the G3Σu+ and 33Σu+ states, the 33Σu+ and 43Σu+ states, the 23Πu and 33Πu states, the g1Πg and 21Πg states, the 23Σg− and 33Σg− states, the 15Πg and 25Πg states, the 25Πg and 35Πg states, the 25Σg− and 35Σg− states, as well as the F3Πg and 33Πg states. Core-valence correlation and scalar relativistic corrections were taken into account. The extrapolation to the complete basis set limit was done. The spectroscopic parameters and vibrational properties were obtained. The transition dipole moments were calculated. Franck-Condon factors of some transitions were evaluated. The spin-orbit coupling (SOC) effect on the spectroscopic parameters and vibrational properties is tiny and sometimes even can be negligible. The results determined in this paper can provide some powerful guidelines to observe these states, in particular the states which have not been studied in the experiment.

Multireference configuration interaction study of ground and low-lying excited states of BrO radical

This work explored the spectroscopic parameters and vibrational properties of 12 states of BrO radical. The 12 states were X2Π, A2Π, 12Δ, 12Σ+, 12Σ−, 22Σ−, a4Σ−, 24Σ−, 14Σ+, 14Δ, 14Π, and 24Π, which were generated from the first dissociation limit, Br(2Pu)+O(3Pg). The potential energy curves were calculated with the CASSCF method, which was followed by the icMRCI approach with Davidson correction. Of the 12 electronic states, the 24Π state was repulsive. Each state had the single well and only the A2Π state had one barrier. The 12Δ, 12Σ+, 12Σ−, 22Σ−, 24Σ−, 14Σ+, 14Δ and 14Π states had only several vibrational levels and were very weakly-bound states, which well depths were less than 110cm−1. To improve the quality of potential energy curves, core-valence correlation and scalar relativistic corrections as well as the extrapolation to the complete basis set limit were included. The spectroscopic parameters and vibrational properties were determined. The transition dipole moments between two electronic states and Franck-Condon factors of some transitions were evaluated. The spin-orbit coupling effect on the spectroscopic parameters of the X2Π and A2Π states was discussed. The spectroscopic parameters and vibrational properties reported in this paper can be expected to be reliably predicted ones.