The spectroscopic and transition properties of the disulfur anion (S2–) were investigated employing the internally contracted multireference configuration interaction method, with spin-orbit coupling effects incorporated via the Breit-Pauli Hamiltonian. Potential energy curves for 24 low-lying Λ-S and 54 Ω states were constructed to determine the spectroscopic parameters of bound and quasi-bound states, which were validated against available experimental data. The X2Πg (υ" = 0‒21) state of S2– is found to be stable at a calculated adiabatic electron affinity of 12738.29 cm‒1 for S2. Furthermore, transition dipole moments between Λ-S states were calculated to predict transition probabilities, including Einstein A coefficients, Franck-Condon factors, and band origins of vibronic emissions. The vibrational radiative lifetimes vary significantly across different electronic states: the A2Πu state exhibits the shortest lifetime (∼0.1 μs), followed by the double-well 12Σu– state (0.1∼1 μs). The 12Δg and 12Σg– states show lifetimes of ∼1 μs, whereas the 12Δu and 12Σu+ states range from 1 to 10 μs. Broader ranges are observed for the 14Πu and 12Σg+ states (1∼100 μs for the former and first well of the latter, 100 μs for the second well of 12Σg+), with the 24Πu state reaching 1000 μs. The radiative lifetimes for the a4Σ–→X2Πg and A2Πu→X2Πg transitions encompassing all relevant Ω components (1/2 and 3/2) were also evaluated.

The potential energy curves of 18 Lambda-S states of the P2(+) cation have been constructed using the internally contracted multi-reference configuration interaction approach combined with the Davidson correction. The basis-set extrapolation to the complete basis set limit is performed. The relativistic effect is considered in calculations. Treatment of scalar relativistic effect at the third-order Dkroll-Hess approximate and spin-orbit coupling with the state-average Breit-Pauli operator is made. Based on the obtained potential energy curves, the spectroscopic parameters for all bound Lambda-S and Omega states are determined. These results are in agreement with experiment where the spectroscopic data are available. The transition dipole moments are calculated. The properties of the dipole-allowed transitions among doublet or quartet Lambda-S states are evaluated, from which Einstein coefficients, Franck-Condon factors and radiative lifetimes are estimated. The spin-orbit coupling effect on the transition properties of the 1(2)Pi(g)-> X-2 Pi(u) system is also studied. The spectroscopic and transition properties reported in this study can be used to guide the detection of phosphorus dimer cation in spectroscopy experiments. GRAPHICAL ABSTRACT

The potential energy curves of 103 Omega states generated from the 39 Lambda-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 Lambda-S and Omega 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 A(1)Pi, b(3)Pi, D-1 Delta, E-1 Sigma(+), and 2(1)Pi states and so on have been revealed.

This work calculated the potential energy curves of the X-1 Sigma(+), I-1 Sigma(-), A(1)Pi, D-1 Delta, B-1 Sigma(+), a(3)Pi, a'(3)Sigma(+), d(3)Delta, and e(3)Sigma(-)states of the carbon monoxide, the transition dipole moments between the X-1 Sigma(+), I-1 Sigma(-), A(1)Pi, D-1 Delta, and B-1 Sigma(+), states, and the transition dipole moments of the a(3)Pi - X-1 Sigma(+) spin-forbidden transition. The calculations were made using the CASSCF method, followed by the icMRCI approach. The radiative lifetime of the first 16 levels was approximately 9.8-11 ns for the A(1)Pi state, 6.3-23.7 ns for the B-1 Sigma(+) state, and 0.24-553 ms for the D-1 Delta state. The Einstein A coefficients, band origins, and Franck-Condon factors of the spontaneous bands from all electric dipole-allowed transitions were calculated. The A(1)Pi - X-1 Sigma(+), B-1 Sigma(+) - X-1 Sigma(+), and B-1 Sigma(+) - A(1)Pi transitions were strong, whereas the A(1)Pi -I-1 Sigma(-) and D-1 Delta - A(1)Pi transitions were weak. The spin-forbidden transition from the a(3)Pi state to the X-1 Sigma(+) state were calculated. The a(3)Pi(1) - X-1 Sigma(+)(0+) transition was much stronger than the a(3)Pi(0+) - X-1 Sigma(+)(0+) transition. The radiative lifetimes of the first 16 vibrational levels were approximately 12.6-25.5 ms and 10-10(5) s for the a(3)Pi(1) and a(3)Pi(0+) states, respectively. The radiative-lifetime distribution depending on J at a certain v was calculated at v <= 15 and J <= 70 for the A(1)Pi and a(3)Pi(1) states. Comparison of the transition properties reported herein with the available measurements shows that these results are accurate.

Ab initio calculations have been performed to study the transition properties of the PS+ cation. Transition dipole moments of fourteen dipole-allowed transitions between the X1Σ+, A1Σ−, B1Δ, C1Π, D1Σ+, E1Π, and F1Σ+ states have been calculated. Transition probabilities, such as Einstein coefficients, Franck-Condon factors, as well as band origins of vibronic emissions involved are predicted. The radiative lifetimes are computed to be in order of 10−8 s for the D1Σ+, F1Σ+, and first well of E1Π states; 10−7 s for the C1Π state; 10−3-10−4 s for the second well of E1Π state. Various curve crossings and avoided crossings are revealed. The intricate couplings among different electronic states are analyzed. The spectral ranges, transition probabilities, radiative lifetimes, and perturbation information reported herein are expected to provide useful guidelines for experimental investigations in the near future.

Ab initio calculations have been performed to study the transition properties of the PS+ cation. Transition dipole moments of fourteen dipole-allowed transitions, between the X-1 Sigma(+), A(1)Sigma(-), B-1 Delta, C-1 Pi, D1 Sigma+, E-1 Pi, and F-1 Sigma(+) states, have been calculated with the aug-cc-pV6Z basis set. Transition probabilities, band origins, as well as radiative lifetimes of vibronic emissions are predicted. The vibrational radiative lifetimes are estimated to be in order of 10(-8) s for the D-1 Sigma(+), F-1 Sigma(+), and first well of E-1 Pi states; 10(-7) s for the C-1 Pi state; 10(-3)-10(-4) s for the second well of E-1 Pi state. Various curve crossings and avoided crossings are revealed with the help of our computed spin-orbit coupling matrix elements. The intricate couplings among different electronic states are analyzed. We propose that the curve crossing with the D-1 Sigma(+) state may be responsible for the fact that the C-1 Pi nu' > 7 vibrational levels cannot be detected in experiment.

In this study, the potential energy curves were calculated for the X-4 Sigma(-), A(4)Pi, B-4 Delta, (CE+)-E-4, (DE-)-E-4, E-4 Pi, a(2)Pi, b(2)Delta, c(2)E(-), d(2)E(+), and e(2)Pi states of silicon boride. The transition dipole moments were computed for all dipole-allowed transitions between these states. The complete active space self-consistent field method was used for calculations, followed by the valence internally contracted multireference configuration interaction approach. The radiative lifetimes were approximately 1 - 10 mu s, 0.1 - 1 mu s, 1 - 10,000 ms, 1 - 1000 ms, and 1 mu s for the A(4)Pi, D-4 Sigma(-), B-4 Delta, C-4 Sigma(+), and Sigma(4)Pi states, respectively. Of these transitions between the six lowest-lying quartets, the spontaneous emissions from the A(4)Pi - X-4 Sigma(-), D-4 Sigma(-) - X-4 Sigma(-), E-4 Pi - X-4 Sigma(-), and E-4 Pi - A(4)Pi systems were strong, whereas those from the B-4 Delta - A(4)Pi, C-4 Sigma(+) - A(4)Pi, and Sigma(4)Pi - B-4 Delta transitions were weak. The radiative lifetimes were approximately 0.1 - 1000 ms, 0.1 - 100 ms, 10 - 100 mu s, and 1 - 10 mu s for the b(2)Delta, c(2)Sigma(-), d(2)Sigma(+), and e(2)Pi states, respectively. Of the transitions between the a(2)Pi, b(2)Delta, c(2)Sigma , d(2)Sigma(+), and e(2)Pi states, the spontaneous emissions from the e(2)Pi - b(2)Delta and e(2)Pi - c(2)Sigma(-) systems were relatively strong, whereas those from the b 2 4 - a 2 1 1 transition were relatively weak. The transition frequencies, Einstein A coefficients, and Franck-Condon factors of all spontaneous vibronic bands from these transitions were calculated. The results obtained in this study were compared with experimental and other theoretical values. The radiative-lifetime distribution varying with rotational angular quantum number J was calculated when J <= 50.5 for a particular vibrational level of these states. (C) 2020 Elsevier Ltd. All rights reserved.

The potential energy curves of the X-1 Sigma(+), A(1) Sigma(-), B-1 Delta, C-1 Pi, a(3) Sigma(+), b(3) Delta, c(3) Pi, and d(3) Sigma(-) states of PO+ and the transition dipole moments between these states were calculated using the CASSCF method, and then the icMRCI approach. To accurately compute the transition properties, core-valence correlation and scalar relativistic corrections were taken into account. The spin-orbit coupling calculations were used to determine the transition properties of the A(1) Sigma(-), B-1 Delta, a(3) Sigma(+), and b(3) Delta states, from which no spontaneous emissions were generated owing to the limitations from the dipole-allowed transition selection rule. The radiative lifetime was approximately 10 - 100 ns for the C-1 Pi state and 10 mu s for the c(3) Pi state. Among these dipole-allowed transitions, the emissions from the C-1 Pi - X-1 Sigma(+) system was the strongest and was followed by the C-1 Pi - A(1)Sigma(-) and c(3) Pi - a(3) Sigma(+) transitions. The radiative lifetime was approximately 10 - 100, 10 - 100, and 100 mu s for the A(1) Sigma(-)(0), d(3) Sigma(-)(0+), and d(3) Sigma(-)(1) states, respectively. Those were of the order of 0.1 - 10, 10, 10 - 100, 1 - 100, and 0.1 - 1 ms for the B-1 Delta(2), a(3) Sigma+(1), a(3) Sigma(+)(0-), b(3)Delta(1), and b(3)Delta(2) states, respectively. Among the spontaneous emissions generated from these Omega states, those from the A(1)Sigma(-)(1) - a(3)Sigma+(0-), A(1)Sigma(-)(1) - a(3)Sigma(+)(1), B-1 Delta(2) - b(3)Delta(3), b(3)Delta(2) - a(3)Sigma+(1), d(3)Sigma(-)(0+) - a(3)Sigma(+)(0-), and d(3)Sigma(-)(1) - a(3)Sigma+(1) transitions were relatively strong. The transition properties reported herein are expected to provide useful guidelines for the detection in future experiments. (C) 2021 Elsevier Ltd. All rights reserved.

The transition dipole moments of the dipole-allowed transitions between the X-2 Sigma(+), A(2)Pi, B-2 Sigma(+), 2(2)Pi, 1(2)Sigma(-), and C-2 Delta states of the carbon monosulfide cation were calculated using the complete active space self-consistent field method, followed by the internally contracted multireference configuration interaction approach. The transition dipole moments of the spin-forbidden transitions from the a(4)Sigma(+) state to the X-2 Sigma+ and A(2)Pi states were computed. The radiative lifetimes were of the order of 1 - 10 mu s, 100 ns, 1 mu s, 10 - 100 mu s, and 1 - 10 mu s for the A(2)Pi, B-2 Sigma(+), 2(2)Pi, 1(2)Sigma(-), and C-2 Delta states, respectively. The transition frequencies, Einstein A coefficients, and Franck-Condon factors of all these spontaneous vibronic emissions from these systems were calculated. The emissions from the A(2)Pi - X-2 Sigma(+), B-2 Sigma(+) - X-2 Sigma+ B-2 Sigma(+) - A(2)Pi, 2(2)Pi - A(2)Pi, and C-2 Delta - A(2)Pi systems were strong, suggesting that the 2(2)Pi state could be measured in a spectroscopy experiment via 2(2)Pi - A(2)Pi transition. Those from the 2(2)Pi - B-2 Sigma(+), 1(2)Sigma(-) - 2(2)Pi, and C-2 Delta - 2(2)Pi systems were weak. The radiative lifetimes of the a(4)Sigma(+)(1/2) and a(4)Sigma(+)(3/)(2 )states were approximately 10 ms. Among these spin-forbidden transitions, the emissions from the a(4)Sigma(+)(3/)(2) - A(2)Pi(3/)(2) system were relatively strong. The radiative-lifetime distribution of each vibrational level versus the rotational quantum number was evaluated for the A(2)II, B-2 Sigma(+), 2(2)Pi, 1(2)Sigma(-), C-2 Delta, and a(4)Sigma(+) states. (C) 2020 Elsevier Ltd. All rights reserved.

The TDMs are calculated for the dipole–allowed transitions between the X1Σ+, I1Σ−, A1Π, D1Δ, and B1Σ+ states of CO and for the a3Π – X1Σ+ spin–forbidden transition. The radiative lifetimes of the vibrational levels are roughly 9.8–11 ns for the A1Π state, 6.3–23.7 ns for the B1Σ+ state, and 0.24–553 ms for the D1Δ state, 12.6–25.5 ms for the a3Π1 state, and 10–105 s for the a3Π0+ and a3Π0– states. The A1Π – X1Σ+, B1Σ+ – X1Σ+, and B1Σ+ – A1Π transitions are strong, whereas the A1Π – I1Σ− and D1Δ – A1Π transitions are weak. The emissions of a3Π0+ – X1Σ+0+ and a3Π0– – X1Σ+0+ systems are much weaker than those from the a3Π1 – X1Σ+0+ transition. The radiative–lifetime variation with J (J ≤ 70) is slow for the A1Π and a3Π1 states.

A number of experiments have been performed to measure the transition properties of the low-lying states of boron monosulfide; however, only a few theoretical results have been reported in the literature. Thus, the transition properties of several of the lowest-lying states are investigated herein. The potential energy curves of the Omega states generated from the X-2 Sigma(+), A(2)Pi, B-2 Sigma(+), C-2 Pi, a(4)Sigma(+), and b(4)Delta states and the transition dipole moments between them were calculated using icMRCI approach. The radiative lifetimes of the first 16 levels were of the order of 9 - 20, 12 - 22, and 1.3 - 6.5 mu s for the A(2)Pi(1/2) , A(2)Pi(3/2), and B-2 Sigma(+)(1/2) states, respectively; those were approximately 361 - 553 and 298 - 513 ns for the C-2 Pi(1/2) and C-2 Pi(3/2) states, respectively. The C-2 Pi(3/2) - X-2 Sigma(+)(1/2) , C-2 Pi(1/2) -X-2 Sigma(+)(1/2), and C-2 Pi(1/2) - A(2)Pi(3/2) transitions were the strongest, followed by the B-2 Sigma(+)(1/2) - A(2)Pi(3/2), B-2 Sigma(+)(1/2) - A(2)Pi(1/2) , and C-2 Pi(3/2) - A(2)Pi(1/2) transitions. The transitions from the a(4)Sigma+ and b(4)Delta states to the X-2 Sigma(+) state were evaluated. The radiative lifetimes of the first 16 levels were of the order of 3.2 - 6.0, 8.9 - 17.3, and 61 - 7644 ms for the a(4)Sigma(+)(3/2) , a(4)Sigma(+)(1/2), and b(4)Delta(5/2), respectively; those were approximately 15 - 1430 and 7 - 1006 mu s for theb(4)Delta(3/2) and b(4)Delta(1)(/2) states, respectively. Among these forbidden transitions, the emissions from the b(4)Delta(1/2) - X-2 Sigma(+)(1/2), b(4)Delta(1/2) - A(2)Pi(3/2), b(4)Delta(1/2) - A(2)Pi(1/2), b(4)Delta(1/2) - X-2 Sigma(+)(1/2) , b(4)Delta(1/2) - A(2)Pi(3/2), and b(4)Delta(1/2) - A(2)Pi(1/2) systems were strong. The distribution of the radiative lifetime at a level upsilon versus the rotational quantum number J was evaluated for the A(2)Pi(1)(/2) , A(2)Pi(3/2), B-2 Sigma(+)(1/2), C-2 Pi(1/2), and C-2 Pi(3/2) states. (C) 2021 Elsevier Ltd. All rights reserved.

Numerous experimental and theoretical investigations studied the transition properties of the A(1)Pi - X-1 Sigma(+) system of carbon monosulfide. However, only a few transition properties are currently available except for the A(1)Pi state. Therefore, this study calculated the properties of the dipole-allowed transitions arising from the 1(1)Sigma(-), 1(1)Delta, 2(1)Sigma(+), a(3)Pi, 1(3)Sigma(+), d(3)Delta, and e(3)Sigma(-) states and the spin-forbidden transition from the a(3)Pi to the X-1 Sigma(+) state. The radiative lifetimes were approximately 10 ns for the 2(1)Sigma(+) state, 10 mu s for the e(3)Sigma(-) state, 10 - 100 mu s for the d(3)Delta state, and 10 - 10 00 mu s for the 1(3)Sigma(+) state. The emissions from the 2(1)Sigma(+) - X-1 Sigma(+) system were strong. The radiative lifetimes were of the order of 0.1 - 1000 ms for the 1(1)Delta state and 0.1 - 105 ms for the 1(1)Sigma(-) state. The lower the vibrational level of the 1(1)Delta and 1(1)Delta- states was, the longer the radiative lifetime became, suggesting that the spontaneous emissions arising from the lower vibrational levels of the two states were difficult to be measured through spectroscopy. The radiative lifetimes were of the order of 1 - 10 and 1 ms for the a(3)Pi(1) and a(3)Pi(0+) states, respectively; whereas those of the a(3)Pi(2) and a(3)Pi(0-) states were extremely long. The radiative-lifetime distribution varying with the rotational angular quantum number J was investigated at J <= 70 for a particular vibrational level of the 1(1)Sigma(-), 1(1)Delta, 2(1)Sigma(+), a(3)Pi, 1(3)Sigma(+), d(3)Delta, e(3)Sigma(-), a(3)Pi(1), and a(3)Pi(0+) states. (c) 2020 Elsevier Ltd. All rights reserved.

ABSTRACT Sulfur monoxide radical has widely been detected in outer space using ground-state spectroscopy. The a 1Δ2 and b 1Σ+0+ states of this radical have low excitation energies, and they possibly exist in outer space. In this work, the potential energy curves and dipole moment functions of the two states were evaluated using the complete active space self- consistent field method, followed by the valence internally contracted multireference configuration interaction approach. The transition line positions, oscillator strengths, band transition dipole matrix elements, Einstein A coefficients, and Franck–Condon factors of all transitions were calculated for lower vibrational levels at rotational angular momentum quantum number J up to 150. The transition line positions calculated in this study are in good agreement with the experimental results. The rovibrational transition became noticeably weak at Δυ > 5. Comparing the results of a 1Δ2 and b 1Σ+0+ states reported in this paper with the previous values, we conclude that these results are the most accurate and complete to date. GRAPHICAL ABSTRACT

This study addresses the transition properties of the X-3 Pi, A(3)Sigma+, B-3 Sigma(-), C-3 Pi, D-3 Pi, E-3 Sigma(+), a(1)Sigma(+), b(1)Pi, c(1)Delta, and d(1)Sigma(+) states of the boron nitride molecule. The potential energy curves and transition dipole moments are calculated using the complete active space self-consistent field method, followed by the valence internally contracted multireference configuration interaction approach. The radiative lifetimes are of the order of 10(-8) s for the E-3 Sigma(+) state, 10(-7)-10(-8) s for the C-3 Pi state, 10(-7) s for the D-3 Pi and d(1)Sigma(+) states, 10(-6) s for the c(1)Delta state, 10(-5)-10(-6) s for the B-3 Sigma(-) state, and 10(-5) s for the A(3)Sigma(+) and b(1)Pi states. The C-3 Pi - X-3 Pi and E-3 Sigma(-)- X-3 Pi transitions are strong, followed by the D-3 Pi - X-3 Pi, D-3 Pi - B-3 Sigma(-), E-3 Sigma(-) - A(3)Sigma(+), d(1)Sigma(+) - a(1)Sigma(+), and d(1)Sigma(+) - b(1)Pi transitions. The spin-forbidden transitions from the a(1)Sigma(+) and b(1)Pi states to the X-3 Pi state are calculated and confirmed to be weak. The radiative lifetimes of all the vibrational levels are approximately 10(-1) s for the a(1)Sigma(+)(0+) state. The contribution of the b(1)Pi - X-3 Pi transition to the radiative lifetimes of the b(1)Pi state is sufficiently insignificant to be considered negligible. The Franck-Condon factors, Einstein A coefficients, and band origins of all the spontaneous vibronic emissions from all these transitions involved herein are calculated. The distribution of the radiative lifetime varying with rotational angular quantum number J is investigated at J <= 70 for a certain vibrational level nu of the A(3)Sigma(+), B-3 Sigma(-), C-3 Pi, D-3 Pi, E-3 Sigma+, b(1)Pi, and c(1)Delta states when nu <= 15. The transition properties reported in this study can provide useful guidelines for future investigations, both experimentally and theoretically. (C) 2020 Elsevier Ltd. All rights reserved.

In this study, we calculated the properties of the transition between six lowest-lying triplet states (X-3 Sigma(-)(g), A'(3)Delta(u), A(3)Sigma(+)(u), B ''(3)Pi(u), B-3 Sigma(-)(u), and B'(3)Pi(g)) of sulphur dimer. The calculations were made with the CASSCF method, followed by the valence icMRCI approach. It was found that the radiative lifetime of the B-3 Sigma(-)(u) state is in the order of 10 ns. The Einstein A coefficients of certain vibronic emissions from the B-3 Sigma(-)(u) - X-3 Sigma(-)(g) system were large, and the radiative lifetimes of the B'Pi(g) and B ''Pi(u) states were found to be in the order of 1 and 10 mu s, respectively. The B'(3)Pi(g) - A'(3)Delta(u), B'(3)Pi(g) - A(3)Sigma(+)(u), and B ''(3)Pi(u) - X-3 Sigma(-)(g) transitions were strong and could be measured by spectroscopy. In contrast, the B'(3)Pi(g) - B ''(3)Pi(u) and B'(3)Pi(g) - B-3 Sigma(-)(u) transitions were weak and therefore, difficult to be detected via spectroscopy. The distributions of the radiative lifetimes with varying rotational angular momentum quantum number were evaluated for some lower vibrational states of the B ''(3)Pi(u), B-3 Sigma(-)(u) , and B'(3)Pi(g) states. The spin-orbit coupling effect on the transition properties of the B ''Pi(u) - X-3 Sigma(-)(g)( )system was also studied. The radiative lifetimes of the B ''(3)Pi(u, 0+), B ''(3)Pi(u, 1), and B ''(3)Pi(u, 2) states were in the order of 10(-6) - 10(-7), 10(-6) - 10(-7), and 10(-5) s, respectively. The transition properties reported in this study can be used to guide the detection of sulphur dimers in both laboratory experiments and astrophysical environments. (C) 2019 Elsevier Ltd. All rights reserved.

Normal emissivity of nickel-cobalt alloys was measured at temperatures from 800 to 1100 K and at 1.5 mu m. When we measured the emissivity, nickel-cobalt specimens were heated to a given temperature and then maintained at that temperature for at least 6 h. To obtain the normal emissivity varying with the thickness of oxidation film at a definite temperature as accurately as possible, the temperature of nickel-cobalt specimens was determined by two thermocouples. The two thermocouples were symmetrically welded onto the front surface of nickel-cobalt specimens. Eleven analytical functions were employed to evaluate the normal emissivity of nickel-cobalt alloys varying with temperature at a definite heating time and its normal emissivity varying with heating time at a given temperature. The influence of the total number of variables in the emissivity analytical models on the fitting quality was investigated. As a conclusion, the fitting quality of normal emissivity could be improved generally by adding the variables to the analytical functions. As a whole, almost all analytical models with four variables can reproduce well the experimental results, whether for a definite heating time or temperature, whereas the analytical models with five variables can reproduce better the measurements. A strong oscillation of emissivity at each temperature was observed. It can be explained by the effect of interference between two optical radiations: one radiation is from the oxide film of specimens; the other coming from the substrate of samples.

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.

Carbon monosulfide was detected in outer space by rovibrational spectroscopy of the X (1)sigma(+) state and A (1)pi - X (1)sigma(+) system. This work calculated the potential energy curves and dipole moment functions of the X (1)sigma(+)(0+) and A (1)pi(1) 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 (1)sigma(+)(0+) and A (1)pi(1) states became very weak when Delta upsilon >= 6. The Einstein A coefficients of vibronic emissions of the A (1)pi(1) - X (1)sigma(+)(0+) system were large, indicating that the emissions were able to be measured easily through spectroscopy. Several rovibrational transitions of the A (1)pi(1) - X (1)sigma(+)(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.

The potential energy curves of 23 states of AlN radical are calculated to accurately determine the first several lowest-lying singlet and triplet states. The calculations are done using the CASSCF method, which is followed by the valence internally contracted MRCI approach. The rotationless radiative lifetimes of the vibrational levels are approximately 10-7-10-8 s for the C3Π, D3Π, and E3Δ states, 101-10-4 s for the A3Σ- state, and 10-4-10-5 s for the B3Σ+ state. The origins of the vibronic bands and the radiative lifetimes agree well with the available experimental and other theoretical results. The Einstein coefficients of many vibronic emissions are large for the C3Π-X3Π, C3Π-A3Σ-, D3Π-X3Π, D3Π-A3Σ-, and E3Δ-X3Π transitions and therefore, these transitions are strong. The emissions of the E3Δ-D3Π system are so weak that it is difficult to measure them through spectroscopy. The spectral distribution of the vibronic emissions is evaluated for the transitions of 12 pairs of states. In terms of the radiative lifetimes and transition probabilities obtained here, several spectroscopic routines for observing these states via spectroscopy are proposed.

In this study, we calculated the potential energy curves of the X-3 Pi, A(3)Sigma(-), B-3 Sigma(+), C-3 Pi, D-3 Delta, and E-3 Pi states of SiC molecules and the transition probabilities between them. The rotationless radiative lifetimes of the vibrational levels are in the order of 10(-5) s for the A(3)Sigma(-) state, 10(-5)-10(-6) s for the B-3 Sigma(+) state, and 10(-6) to 10(-7) s for the C-3 Pi and E-3 Pi states. This suggests that the spontaneous emissions originating from these states can easily occur. The rotationless radiative lifetimes vary in the range of 10(-3)-10(-5) s for the vibrational levels of the D-3 Delta state. The lifetime of the D-3 Delta, state rapidly decreases with the increasing vibrational level, indicating that the occurrence of spontaneous emissions originating from this state at lower levels is more inhibited than those at higher levels. The emissions of the A(3)Sigma(-)-X-3 Pi, B-3 Sigma(+)-X-3 Pi, C-3 Pi-X-3 Pi, C-3 Pi-A(3)Sigma(-), D-3 Delta-X-3 Pi, and E-3 Pi-X-3 Pi system are strong, suggesting that these transitions can be measured easily by spectroscopy. The emissions of the D-3 Delta-C-3 Pi and E-3 Pi-D-3 Delta systems are weak, suggesting that these transitions are difficult to detect by spectroscopy. The spectral range of the strong emissions from the A(3)Sigma(-)-X-3 Pi system is in the infrared region. The strong emissions of the B-3 Sigma(+)-X-3 Pi, C-3 Pi-X-3 Pi, and C-3 Pi-A(3)Sigma(-) systems are of visible light. Some of these strong emissions, especially those from the A(3)Sigma(-)-X-3 Pi system, could be expected to be detectable in carbon star IRC + 10,126 and the circumstellar shell. (C) 2019 Elsevier Ltd. All rights reserved.