Radiative Lifetimes Of Vibrational Levels Research Articles

Spectroscopic investigations of transition properties for the electronic states of PN+ correlating to two lowest dissociation limits

The PN+ cation is regarded as a candidate of ions which may exist in the interstellar medium. Accurate transition properties are desired to identify the spectra from astronomical observation. However, transition data of PN+ are relatively limited. In this work, the state-of-the-art ab initio calculations are carried out to investigate the low-lying electronic states of PN+ correlating to two lowest dissociation limits, its transition properties and its spin-orbit couplings. For the X2Σ+ and A2Π states, the calculated spectroscopic constants agree well with previous experimental data. For the other electronic states, the accuracy of the spectroscopic parameters is also ensured by comparing with previous theoretical results. Then, transition probabilities of dipole allowed transition systems are calculated. The radiative lifetimes of vibrational levels for the A2Π, 14Π, 14Δ, 14Σ−, and 24Π states are also evaluated. Such transition data can be used in the identification of PN+ in the laboratory or the interstellar space. Finally, the predissociation of 14Σ− (υ' = 1)→16Σ+, 14Σ− (υ' = 15)→16Π and 14Δ (υ'= 19)→16Π are analyzed with the help of spin-orbit coupling integrals.

Radiative lifetimes of vibrational levels and transition probabilities of spontaneous emissions of the six lowest-lying triplet states of AlN radical.

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.

Transition Probabilities of Emissions and Rotationless Radiative Lifetimes of Vibrational Levels for the SiN Radical

Abstract The transition dipole moments of the SiN radical are calculated by the valence internally contracted multireference configuration interaction (icMRCI) approach with the aug-cc-pV6Z basis set. The transition probabilities of spontaneous emissions are computed between the eight lowest-lying doublet states. The vibrational band origins, Einstein coefficients, and Franck–Condon factors of all the spontaneous emissions involved are evaluated. The rotationless radiative lifetimes of the first 15 vibrational levels were determined to be approximately 10−3–10−5 s long for the A2Π state, 10−3–10−7 s long for the F2Π state, 10−6–10−7 s long for the C2Π state, 10−6 s long for the D2Σ− and E2Δ states, and 10−7 s long for the B2Σ+ and G2Δ states. It is observed that the rotationless radiative lifetimes quickly become shorter, with an increase in the vibrational level for the A2Π and F2Π states. The Einstein coefficients of many emissions are large for the B2Σ+–X2Σ+, B2Σ+–A2Π, C2Π–X2Σ+, C2Π–A2Π, D2Σ−–A2Π, E2Δ–A2Π, F2Π–X2Σ+, F2Π–A2Π, and G2Δ–A2Π systems. However, the emissions are very weak for the F2Π–D2Σ− system. The vibrational levels and rotational constants of each state are determined and the spectral range of each transition system is evaluated. The vibrational band origins are compared with the available experimental ones. The spectroscopic routines for detecting the unobserved states are proposed. These results can be employed to measure emissions, in particular those of interstellar clouds and stellar atmospheres.

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.

Transition Probabilities of Emissions and Rotationless Radiative Lifetimes of Vibrational Levels for the PO Radical

Abstract This work investigates the transition dipole moments (TDMs) and transition probabilities of electric dipole emissions between the X2Π, B2Σ+, B′2Π, D′2Π, C2Σ−, C′2Δ, F2Σ+, and P2Π states of the PO radical. The TDMs of 23 pairs of states are calculated by the internally contracted multireference configuration method with the aug-cc-pV6Z basis set. The vibrational band origins, Franck–Condon factors, and Einstein coefficients of all the spontaneous emissions are evaluated. The rotationless radiative lifetimes of the vibrational levels are approximately 10−7–10−8 s for the B2Σ+, C2Σ−, C′2Δ, P2Π, and F2Σ+ states; 10−4–10−5 s for the B′2Π state; and 10−1–10−2 s for the D′2Π state. The Einstein coefficients of many emissions are large for the B2Σ+–X2Π, B′2Π–X2Π, C′2Δ–X2Π, C2Σ−–X2Π, F2Σ+–X2Π, P2Π–X2Π, P2Π–B′2Π, and P2Π–D′2Π systems. Almost all the spontaneous emissions arising from the D′2Π state are very weak. The vibrational band origins of these emissions extend from the UV into the far-infrared spectra. The radiative lifetimes and vibrational band origins are compared with available experimental and theoretical values. According to the radiative lifetimes and transition probabilities obtained in this paper, some guidelines for detecting these states spectroscopically are proposed. The TDMs and transition probabilities reported here are considered to be reliable and can be used as guidelines for detecting similar transitions, especially those in interstellar space.

Calculation of radiative parameters for the $$ {A^1}\sum\nolimits_u^{+} {{X^1}} \sum\nolimits_g^{+} {} $$ -transition of cesium dimer

Radiative parameters for vibrational bands (0 ≤ v′ ≤ 30, 0 ≤ v′′ ≤ 59) of the $$ {A^1}\sum\nolimits_u^{+} {{X^1}} \sum\nolimits_g^{+} {} $$ -electronic transition of a cesium dimer are calculated. These include vibronic band wavenumbers, Franck–Condon factors, Einstein coefficients for spontaneous emission, absorption band oscillator strengths, and radiative lifetimes for vibrational levels of the excited electronic state. Vibrational energies and wave functions for the ground and excited electronic states were found by a numerical solution of the radial wave equation based on potential curves plotted during the course of the study.

Electronic structure and fluorescence spectrum of the HeO+ cation

Quantum-mechanical calculations of the potential curves of the HeO+ ion are preformed which correlate with four lower dissociation limits and indicate the excimer type of the ion. The transition dipole moments of the 22Σ−→12Σ− and 24Σ−→14Σ − transitions are calculated. The energies and radiative lifetimes of vibrational levels are determined and structural and spectroscopic constants of the states 12Σ−, 22Σ−, 14Σ−, and 24Σ− are calculated. The fluorescence spectrum corresponding to the 22Σ−→12Σ− and 24Σ−→14Σ − transitions is also calculated. The possibility of lasing at these transitions is discussed.

Experimental investigation of radiative lifetimes of vibrational levels at the electronic ground state of C2−

Radiative lifetimes of the vibrational levels v=2 to v=4 of the X 2Σg+ ground state of the C2− molecular ion have been experimentally investigated by photodetachment in a storage ring. The lifetime of the v=3 level was 0.32±0.02 s for 12C12C−, and 0.22±0.02 s for 12C13C−. For both ions, the lower limit for the v=2 lifetime was 5 s, and the upper limit for the v=4 level was ∼100 ms. The measured lifetime for v=3 of 12C12C− is a factor of 4 smaller than found in a calculation [P. Rosmus and H. Werner, J. Chem. Phys. 80, 5085 (1984)]. The results point to the existence of at least one bound vibrational level of the lowest 4Σu+ state.

Theoretical radiative transition probabilities of the CS + ion

The electronic transition moment functions for the A 2Π-X 2Σ +, B 2Σ +-X 2Σ +, B 2Σ +-A 2Π and C 2Δ-A 2Π transitions were calculated from highly correlated CASSCF CI electronic wavefunctions and used for the evaluation of the radiative lifetimes and absorption oscillator strengths. For the B 2Σ +, ν′=0 state the calculated lifetime of 364 ns is found to be in good agreement with the experimental value of 425 ± 25 ns. The variations of the radiative lifetimes with vibrational quantum number in the A, B and C states of CS + are predicted. These theoretical lifetimes are expected to be accurate w within about 20%. The dipole moment of the X 2Σ +, ν=0 state is calculated to be 0.509 ± 0.05 D. The radiative lifetimes of vibrational levels in the electronic ground state are also given. For the C 2Δ state spectroscopic constants are predicted.

Theoretical study of low-lying 1Σ− and 1Δ states of CO

A b initio calculations of electronic wave functions and potential energy curves for each of two low-lying states of 1Σ− and 1Δ symmetry for CO are reported. The second state of each symmetry has Rydberg character. Computed spectroscopic constants for the metastable I 1Σ− and D 1Δ states appear to be in good agreement with experimental data. The radiative lifetimes of vibrational levels within the I 1Σ− and D 1Δ states have been computed considering two types of decay: cascade within each electronic state, and transitions to the nearby A 1Π. It is shown that the v=0 levels of each metastable electronic state have very long lifetimes. The observation of these metastable states in electron impact experiments is discussed in light of our results.

Theoretical and experimental studies of radiative lifetimes of excited electronic states in CO+

The electronic dipole transition moment functions of the A 2Π-X 2Σ+, B 2Σ+-X 2Σ+ and B 2Σ+-A 2Π transitions and the dipole moment function of the X 2Σ+ state of CO+ have been calculated using large contracted CI wavefunctions. The computed transition moment functions together with experimental potential energy curves were used to obtain radiative lifetimes of the excited electronic states B 2Σ+ and A 2Π. Radiative lifetimes of vibrational levels of the X 2Σ+ state were derived from the calculated dipole moment function. The high-frequency deflection technique was used to obtain radiative lifetimes of the ν′ = 0, 1,2 and 3 vibrational levels of the B 2Σ+ state and also radiative lifetimes of individual rotational levels of ν′ =0. The calculated radiative lifetimes are shorter than the measured ones by about 10%. The experimental ν′ dependence is reproduced by theoretical calculation. The calculated radiative lifetimes for the A 2Π state are in excellent agreement with lifetimes measured with an ion trap technique.

Non-orthonormal basis calculations of the dipole transition moment for the phillips system (A 1Π u → X 1Σ +g) in C 2. Theoretical lifetime of the A 1Π u state

Non-orthonormal basis calculations have been carried out on the A 1Π u → X 1Σ + g transition moment of C 2 as a function of CC internuclear distance. Two types of AO basis set and different sizes of CI vectors were employed in order to examine the convergence of the theoretical results. Published ab initio potential energy curves and the transition moments of the present work were combined to calculate radiative lifetimes of vibrational levels of the A 1Π u state. The resulting lifetimes are in agreement with other theoretical values, obtained with orthonormal basis calculations, which however, are significantly lower than those of the most recent experiments.

Time-resolved spectroscopy of the C2 Phillips system and revised interstellar C2 abundances

Radiative lifetimes of vibrational levels of the C/sub 2/A/sup 1/Pi/sub u/ state have been measured by the high frequency deflection technique. The mean lifetime for levels v' = 3, 4, 6, and 7 is 11 ..mu..s. The results are used to deduce the absorption oscillator strengths of the Phillips (A/sup 1/Pi/sub u/- X/sup 1/..sigma../sub g//sup +/) system. The value f/sub 2,0/ = (8.8 +- 1.2) x 10/sup -4/ has been used to revise published estimates of the interstellar C/sub 2/ column density.

Radiative lifetimes for vibrational levels of the B 1Σ state of 7LiH

Newly calculated radiative transition probabilities for the B 1Σ→X 1Σ+ and A 1Σ+ emission bands of 7LiH (preceding paper) are used to calculate the radiative lifetime of the various vibrational levels (0⩽v′⩽2) of B 1Π LiH. An estimate of the B→X bound–free emission probability is also included, although the lifetimes are dominated by the B→X bound–bound emission. The calculated radiative lifetimes increase rapidly with v′ from 11.3 nsec at v′=0 to 17.0 nsec at v′=1 and then 24.0 nsec at v′=2.