Einstein Coefficients Research Articles

Energy levels, transition dipole moment, transition probabilities and radiative lifetimes for low-lying electronic states of PN

The valence internally contracted multireference configuration-interaction (icMRCI) method is used to compute potential energy curves (PECs) of the X1Σ+, A1Π, C1Σ−, D1Δ, 21Π, a3Σ+, b3Π, d3Δ, e3Σ−, 23Δ, 23Σ−, 15Σ+ and 15Π states for PN, together with the Davidson, core-valence (CV) and scalar relativistic corrections, as well as the basis-set extrapolation. Transition dipole moments (TDMs) of fifteen dipole-allowed transitions between the thirteen states are calculated by the icMRCI approach with the aug-cc-pV6Z basis set. The vibrational band origins, Einstein coefficients and Franck-Condon factors of all spontaneous emissions for the fifteen band systems are determined, seeking to theoretically predict the strong emissions at least of the order of 103 s−1 for Einstein coefficients. Comparing with experimental measurements, our calculations can well reproduce the band origins and Franck-Condon factors of the A1Π-X1Σ+ system. Similar accuracy is assumed for the other band systems. Many emissions for the A1Π-X1Σ+, 21Π-A1Π, 21Π-X1Σ+, 21Π-C1Σ−, 21Π-D1Δ, b3Π-a3Σ+, e3Σ−-b3Π, 23Δ-13Δ, 23Σ−-13Σ−, 23Σ−-b3Π and 15Π-15Σ+ systems are found to be strong according to our calculated Einstein coefficients, whereas the emissions are weak for the 23Δ-b3Π system. Radiative lifetimes for the first 15 vibrational levels are evaluated to be about tens of nanoseconds for the 21Π state, about several hundred nanoseconds for the A1Π state, about several to tens of microseconds for the b3Π, 23Δ, 23Σ− and 15Π states and about several to several hundred microseconds for the e3Σ− state. The results can be used as guidelines for line identification and diagnostics of astrophysical plasma.

Electronic structure with dipole moment and rovibrational calculations of the MgLi and MgNa molecules

We investigate an orderly study of the adiabatic potential energy curves for 29 and 30 low-lying 2s+1Λ+/− electronic states of the molecules MgLi and MgNa, respectively. The calculation has been done by using the complete active space self-consistent field followed by multi-reference configuration interaction with Davidson correction. For the investigated electronic states, the static and transition dipole moment curves are calculated along with the Einstein coefficients, the emission oscillator strength, the spontaneous radiative lifetime, the line strength, the classical radiative decay rate of the single-electron oscillator, the spectroscopic constants (Te, ωe, ωexe, Be, Re), and the equilibrium dissociation energy De. By means of the canonical functions approach, the ro-vibrational constants Ev, Bv, Dv, and the abscissas of the turning points, Rmin and Rmax, have been calculated for the considered electronic states up to the vibrational level v = 79. The Franck–Condon factors have been calculated and plotted for the transition between the low-lying electronic states of the two considered molecules. A good agreement is revealed between our calculated values and those available in the literature. Fifty new electronic states are investigated in the present work for the first time.

Electronic Structure with Dipole Moment and Rovibrational Calculation of Cadmium Chalcogenide Molecules CdX (X = Se, Te).

Ab initio calculations of 51 electronic states in the representation 2s+1Λ(±) of CdX (X = Se, Te) molecules have been carried out by using the complete active space self-consistent field and multireference configuration interaction (single and double excitations with the Davidson correction). The potential energy along with the static and transition dipole moment curves for the investigated electronic states of the CdX molecules has been mapped. Consequently, the spectroscopic constants Re, ωe, Be, and Te have been computed for the bound states. The spectroscopic dissociation energy De, the zero-point energy, and the ionicity are also calculated for the bound electronic states X3Π, (1)1Σ+, (1)1Π, and (1)3Σ+. Rovibrational calculation is performed for the X3Π, (1)1Σ+, (1)1Π, and (1)3Σ+ states of CdSe together with the X3Π, (1)1Σ+, and (1)1Π states of a CdTe molecule. The Einstein coefficients of spontaneous and induced emissions, A21 and B21, are computed for the transition between the electronic states (1)3Σ+ and X3Π. In the present work, the values are well-consistent with those available in the literature.

Radiative transition probabilities between low-lying electronic states of N2

ABSTRACTThis work mainly investigates the transition dipole moments (TDMs) and radiative transition probabilities of dipole-allowed transitions between the , , , , , , , , and states of N2. Many of these transition properties are previously unknown. For completeness, another 14 electronic states that correlate to four lowest dissociation limits are also calculated. The potential energy curves (PECs) are calculated at the valence internally contracted multireference configuration-interaction (icMRCI) level of theory, along with the Davidson correction, the core-valence (CV) correction and the scalar relativistic correction, as well as the basis-set extrapolation. These corrections, especially the CV correction, greatly improve the accuracy of the PECs, as shown by the excellent agreement of the fitted spectroscopic parameters with the available experimental data. In order to verify the accuracy of transition properties, we calculate the Einstein coefficients of the extensively studied band transition systems and compute the radiative lifetimes of states, which are in good agreement with the experimental data. Similar accuracy can be assumed for the previously undetermined band transition systems. The large Einstein coefficients of these band systems can provide guidelines for observing such newly predicted band transitions in the appropriate spectroscopy experiments.

Theoretical study of laser cooling of potassium chloride anion

The potential energy curves and transition dipole moments (TDMs) for three Λ-S states (X<sup>2</sup>Σ<sup>+</sup>, A<sup>2</sup>Π, and B<sup>2</sup>Σ<sup>+</sup>) of potassium chloride anion (KCl<sup>–</sup>) are investigated by using multi-reference configuration interaction (MRCI) method. The def2-AQZVPP-JKFI of K atom and AV5Z-DK all-electron basis set of Cl atom are used in all calculations. The Davidson correction, core-valence (CV) correction, and spin-orbit coupling effect (SOC) are also considered. In the complete active self-consistent field (CASSCF) calculations, eight molecular orbitals are selected as active orbitals, which includ K 4s4p and Cl 3s3p shells; K 3p shell is closed orbital, and the remaining shells (K 1s2s3s and Cl 1s2s2p) are frozen orbitals. In the MRCI+<i>Q</i> calculations, K 3p shell is used for the CV correction. There are 15 electrons in the correlation energy calculations. Then, their spectroscopic parameters, Einstein coefficients, Franck-Condon factors, and radiative lifetimes are obtained by solving the radial Schrödinger equation. The spectroscopic properties and transition properties for the Ω states are predicted. Highly diagonally distributed Franck-Condon factor <i>f</i><sub>00</sub> values for the (2)1/2↔(1)1/2 and (1)3/2↔(1)1/2 transition are 0.8816 and 0.8808, respectively. And the short radiative lifetimes for the (2)1/2 and (1)3/2 excited states are also obtained, i.e. <i>τ</i>[(2)1/2] = 45.7 ns and <i>τ</i>[(1)3/2] = 45.5 ns, which can ensure laser cooling of KCl<sup>–</sup> anion rapidly. The results indicate that the (2)1/2↔(1)1/2 and (1)3/2↔(1)1/2 quasicycling transitions are suitable to the building of laser cooling projects. For driving the (2)1/2↔(1)1/2 transition, a main pump laser (λ<sub>00</sub>) and two repumping lasers (λ<sub>10</sub> and λ<sub>21</sub>) are required. Their wavelengths are λ<sub>00</sub> = 1065.77 nm, λ<sub>10</sub> = 1090.13 nm and λ<sub>21</sub> = 1087.76 nm. For driving the (1)3/2↔(1)1/2 transition, the wavelengths are λ<sub>00</sub> = 1064.24 nm, λ<sub>10</sub> = 1088.54 nm, and λ<sub>21</sub> = 1086.17 nm. The cooling wavelengths of KCl<sup>-</sup> anion for two transitions are both deep in the infrared range. Finally, the Doppler temperature and recoil temperature for two transitions are also calculated, respectively. The Doppler temperatures for (2)1/2↔(1)1/2 and (1)3/2(1)1/2 transitions are 83.57 μK and 83.93 μK, and the recoil temperatures for two transitions are 226 nK and 227 nK, respectively. for two transitions are 226 nK and 227 nK, respectively.

Внутридопплеровские резонансы, обусловленные осцилляциями Раби на атомных переходах в тонких газовых ячейках

Theoretical research is carried out of excitation of atoms from the ground quantum level to a metastable state by the running monochromatic radiation in thin gas cell, whose inner thickness is much less than its radius. As a result, sub-Doppler resonances has been discovered and analyzed, which appear in the population of the metastable atomic level at scan of the radiation frequency because of light induced Rabi oscillation on the given optical transition and also transit relaxation of atoms in the considered cell with the rarefied gas. Such nontrivial resonances may be detected in atomic fluorescence by additional probe light beam. The method for direct measurement of the Rabi frequency on spectral intervals between established sub-Doppler resonances is proposed. Obtained results may be applied in atomic spectroscopy for precise determination of components of matrix elements of dipole moments and related Einstein coefficients and oscillator strengths of quantum transitions between ground and metastable atomic levels.

Transition probabilities of the seven lowest–lying singlet states of the AlN radical

In this study, the potential energy curves are calculated for the a1Σ+, b1Π, c1Δ, d1Σ+, e1Π, f1Δ, and g1Σ− states of the AlN radical. The transition dipole moments between them are computed. The rotationless radiative lifetimes of the vibrational levels are found to be approximately several µs for the d1Σ+ and g1Σ− states, on the order of several hundred ns for the e1Π state, and one-tenth to several µs for the deep well of the f1Δ state. These results suggest that the spontaneous emissions originated from these states occur readily. The rotationless radiative lifetimes of the vibrational levels are on the order of 10–100 µs for the c1Δ state, 1000 µs for the vdW minimum of the f1Δ state, and 10–1000 µs for the b1Π state. In addition, the rotationless radiative lifetimes of these states decrease with the increasing vibrational level. This result suggests that the spontaneous emissions generated from these states at lower levels should be difficult to occur. The Einstein coefficients of spontaneous emissions from the d1Σ+–a1Σ+, d1Σ+–b1Π, e1Π–a1Σ+, e1Π–b1Π, and g1Σ−–b1Π systems, as well as from the f1Δ state to the b1Π and c1Δ states are large, indicating that the emissions of these systems can be measured readily via spectroscopy. The Einstein coefficients of the e1Π–d1Σ+ transition are very small and the emissions originating from the vdW minimum of the f1Δ state are very weak, predicting that these transitions are very difficult to be detected in spectroscopy experiments.

Rotationless radiative lifetimes and transition probabilities of some low-lying quintet states of the NS+ cation

Recently, the NS+ cation has been detected via spectroscopy as an interstellar species. To determine its transition properties, the potential energy curves of one singlet state and seven quintet states are investigated. For the eight states, 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 spectroscopic parameters and transition dipole moments are compared with the available experimental and other theoretical results. The band origins, Franck–Condon factors, and Einstein coefficients of the spontaneous emissions are calculated for the transitions of 15 pairs of quintet states. It is found that the 15Π–15Σ+, 25Σ+ –15Σ+, 25Π–15Σ+, and 35Σ+–15Σ+ transitions can be detected in a spectroscopy experiment. The rotationless radiative lifetimes of the vibrational levels are approximately 10−5 to 10−6 s for the 25Σ+ state, 10−5 s for the 15Π state, and 10−4–10−5 s for the 35Σ+ and 25Π states. The radiative lifetimes of the vibrational levels are so long that it is rather difficult for the spontaneous emissions generated from the 15Δ and 25Δ states to occur, and the emissions from the two states are very difficult to observe via spectroscopy. The reasons may be that both the 15Δ and 25Δ states have long internuclear equilibrium separations, and the transition dipole moments originating from them are very small. The results reported in this work can be used to detect the NS+ cation in cold molecular clouds, prestellar cores, and shocks.

Quantitative comparison of evaluation indices for asphalt–filler interaction ability within filler critical volume fraction

Asphalt–filler interaction plays a key role in the performances of asphalt mastic and asphalt mixture. However, the current studies ignore the filler critical volume fraction that has significant effects on asphalt–filler interaction ability. There is also lacking quantitative comparison of evaluation indices within filler critical volume fraction. In this study, two kinds of virgin asphalt binders and three kinds of mineral fillers were selected to fabricate asphalt mastics, and the dynamic shear rheological properties of virgin asphalt binders and asphalt mastics were measured, and the interaction evaluation indices complex viscosity coefficient Δη*, intrinsic viscosity [η], complex modulus coefficient ΔG*, K-B-G*, Einstein coefficient KE, L-A-δ and K-B-δ were quantitatively compared. The results indicate that complex viscosity coefficient Δη* and intrinsic viscosity [η] are not suitable for evaluation of asphalt–filler interaction ability. ΔG* and K-B-G* can evaluate the differences of asphalt and different fillers interaction ability based on the same kind of asphalt binder. Nevertheless, ΔG* and K-B-G* cannot differentiate the effects of asphalt binder on asphalt–filler interaction ability well. Although Einstein coefficient KE can evaluate asphalt–filler interaction ability, the Einstein coefficient KE is fitting results, and cannot distinguish the interaction ability under different filler volume fractions. L-A-δ and K-B-δ can differentiate the interaction ability of different asphalt binders and fillers well, and also the sensitivity factors of index K-B-δ are greater than L-A-δ. Therefore, K-B-δ is the most suitable for evaluating asphalt and filler interaction ability. Based on the evaluation index K-B-δ, asphalt–filler interaction ability increases initially and decreases afterwards with an increase in filler concentration within filler critical volume fraction.

Cross section of curvature radiation absorption

When treating the absorption of light, it is instructive to focus on the absorption coefficient related to the probability of photons to survive while traversing a layer of material. From the point of view of particles doing the absorption, however, the elementary interaction of the particle with the photon is best described by the corresponding cross section. We revisit curvature radiation in order to find the absorption cross section for this process, making use of the Einstein coefficients and their relations with spontaneous and stimulated emission and true absorption. We derive the cross section as a function of the emission angle ψ (i.e. the angle between the instantaneous velocity vector and the direction of the photon) and the cross section integrated over angles. Both are positive, contrary to the synchrotron case for which the cross section can be negative for large ψ. Therefore, it is impossible to have curvature radiation masers. This has important consequences for sources of very large brightness temperatures that require a coherent emission process, such as pulsars and fast radio bursts.

Synthetic spectra of BeH, BeD and BeT for emission modeling in JET plasmas

A theoretical model for isotopologues of beryllium monohydride, BeH, BeD and BeT, A to X visible and X to X infrared rovibronic spectra is presented. The MARVEL procedure is used to compute empirical rovibronic energy levels for BeH, BeD and BeT, using experimental transition data for the X , A , and C states. The energy levels from these calculations are then used in the program Duo to produce a potential energy curve for the ground state, X , and to fit an improved potential energy curve for the first excited state, A , including a spin–orbit coupling term, a Λ-doubling state to state (A–X states) coupling term, and Born–Oppenheimer breakdown terms for both curves. These, along with a previously computed ab initio dipole curve for the X and A states are used to generate vibrational-rotational wavefunctions, transition energies and A-values. From the transition energies and Einstein coefficients, accurate assigned synthetic spectra for BeH and its isotopologues are obtained at given rotational and vibrational temperatures. The BeH spectrum is compared with a high resolution hollow-cathode lamp spectrum and the BeD spectrum with high resolution spectra from JET giving effective vibrational and rotational temperatures. Full A–X and X–X line lists are given for BeH, BeD and BeT and provided as supplementary data on the ExoMol website.

Suggestion for search of silanone (H2SiO) in interstellar medium

Thirteen silicon bearing molecules are detected in the cosmic objects. Carbon (C) and silicon (Si) elements have similar chemical properties and the formaldehyde (H2CO) is identified in a large number of cosmic objects. Hence, there is a possibility of Silanone (H2SiO) being present in the ISM. For each of the ortho and para species of H2SiO, we have calculated energies of 100 lower rotational levels (up to 284 cm−1) and the Einstein coefficients for radiative transitions between the levels. We have solved a set of 100 statistical equilibrium equations coupled with the equations of radiative transfer for each specie where the collisional rate coefficients are taken from a scaling law. For the ortho-H2SiO, five transitions, 110-111, 211-212,312-313,413-414 and 514-515 are found to show the anomalous absorption, and one transition 212-111 is found to show the emission feature. For the para-H2SiO, four transitions, 101-000,202-101,660-514 and 661-542 are found to show the emission feature. These lines may help in the identification of H2SiO in a cosmic object, e.g., in IRC+10216.

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.

Mechanisms for varying non-LTE contributions to OH rotational temperatures from measurements and modelling. II. Kinetic model

OH rotational temperatures Trot deviate from kinetic temperatures Tkin if the rotational level populations derived from the measured OH lines are not in local thermodynamic equilibrium (LTE). In particular,. from OH bands wi Trot th high upper vibrational level appear to be affected by incomplete rotational relaxation and corresponding non-LTE temperature excesses ΔTNLTE. The processes that lead to these non-LTE effects and their variations have not been investigated in detail so far since this requires thorough modelling of the rotational relaxation based on suitable observing data. We performed such an effort for the vibrational level v=9. As it is the highest v that can be populated by the OH-producing hydrogen–ozone reaction, the relaxation processes are the least complex ones. Nevertheless, there are many systematic uncertainties. Therefore, we studied the ΔTNLTE depending on the Einstein A-coefficients used, the very uncertain rate coefficient for the v=9 deactivating collisions of OH with atomic oxygen, and the input profiles for Tkin, air density, and the volume mixing ratios of N2, O2, O, and O3. For the profiles, we used SABER products, where we adapted the O retrieval for a better agreement with the model, and the empirical NRLMSISE-00 model. The profiles were selected or calculated for the Cerro Paranal region in Chile since this allowed us to combine OH Trot measurements based on high-resolution spectra of the UVES spectrograph at the Very Large Telescope with the SABER Tkin and OH emission profiles for an alternative, fully observation-based ΔTNLTE derivation. Moreover, we measured OH(v=9) rotational level populations up to the rotational state N=10 based on UVES OH(9-3) and OH(9-4) line measurements. With these data in comparison with a grid of models, we derived the best-fitting crucial rate coefficients for the rotational relaxation at v=9, which have not been studied before. With the final models, we calculated ΔTNLTE climatologies and compared them with those from the UVES-based data. Significant ΔTNLTE and similar variability structures could be identified. Moreover, we analysed the model in order to find the mechanisms that cause the variations. Here, the steep increase of ΔTNLTE with altitude combined with the height variations of the OH layer appears to be the most important process.

Efficient Brownian Dynamics of rigid colloids in linear flow fields based on the grand mobility matrix.

We present an efficient general method to simulate in the Stokesian limit the coupled translational and rotational dynamics of arbitrarily shaped colloids subject to external potential forces and torques, linear flow fields, and Brownian motion. The colloid's surface is represented by a collection of spherical primary particles. The hydrodynamic interactions between these particles, here approximated at the Rotne-Prager-Yamakawa level, are evaluated only once to generate the body's (11 × 11) grand mobility matrix. The constancy of this matrix in the body frame, combined with the convenient properties of quaternions in rotational Brownian Dynamics, enables an efficient simulation of the body's motion. Simulations in quiescent fluids yield correct translational and rotational diffusion behaviour and sample Boltzmann's equilibrium distribution. Simulations of ellipsoids and spherical caps under shear, in the absence of thermal fluctuations, yield periodic orbits in excellent agreement with the theories by Jeffery and Dorrepaal. The time-varying stress tensors provide the Einstein coefficient and viscosity of dilute suspensions of these bodies.

Development of a High-Resolution Laser Absorption Spectroscopy Method with Application to the Determination of Absolute Concentration of Gaseous Elemental Mercury in Air.

Isotope dilution-cold-vapor-inductively coupled plasma mass spectrometry (ID-CV-ICPMS) has become the primary standard for measurement of gaseous elemental mercury (GEM) mass concentration. However, quantitative mass spectrometry is challenging for several reasons including (1) the need for isotopic spiking with a standard reference material, (2) the requirement for bias-free passive sampling protocols, (3) the need for stable mass spectrometry interface design, and (4) the time and cost involved for gas sampling, sample processing, and instrument calibration. Here, we introduce a high-resolution laser absorption spectroscopy method that eliminates the need for sample-specific calibration standards or detailed analysis of sample treatment losses. This technique involves a tunable, single-frequency laser absorption spectrometer that measures isotopically resolved spectra of elemental mercury (Hg) spectra of 6 1S0 ← 6 3P1 intercombination transition near λ = 253.7 nm. Measured spectra are accurately modeled from first-principles using the Beer-Lambert law and Voigt line profiles combined with literature values for line positions, line shape parameters, and the spontaneous emission Einstein coefficient to obtain GEM mass concentration values. We present application of this method for the measurement of the equilibrium concentration of mercury vapor near room temperature. Three closed systems are considered: two-phase mixtures of liquid Hg and its vapor and binary two-phase mixtures of Hg-air and Hg-N2 near atmospheric pressure. Within the experimental relative standard uncertainty, 0.9-1.5% congruent values of the equilibrium Hg vapor concentration are obtained for the Hg-only, Hg-air, Hg-N2 systems, in confirmation with thermodynamic predictions. We also discuss detection limits and the potential of the present technique to serve as an absolute primary standard for measurements of gas-phase mercury concentration and isotopic composition.

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.

Transition Dipole Moments and Transition Probabilities of the CN Radical

Abstract This paper studies the transition probabilities of electric dipole transitions between 10 low-lying states of the CN radical. These states are X2Σ+, A2Π, B2Σ+, a4Σ+, b4Π, 14Σ−, 24Π, 14Δ, 16Σ+, and 16Π. The potential energy curves are calculated using the CASSCF method, which is followed by the icMRCI approach with the Davidson correction. The transition dipole moments between different states are calculated. To improve the accuracy of potential energy curves, core–valence correlation and scalar relativistic corrections, as well as the extrapolation of potential energies to the complete basis set limit are included. The Franck–Condon factors and Einstein coefficients of emissions are calculated. The radiative lifetimes are determined for the vibrational levels of the A2Π, B2Σ+, b4Π, 14Σ−, 24Π, 14Δ, and 16Π states. According to the transition probabilities and radiative lifetimes, some guidelines for detecting these states spectroscopically are proposed. The spin–orbit coupling effect on the spectroscopic and vibrational properties is evaluated. The splitting energy in the A2Π state is determined to be 50.99 cm−1, which compares well with the experimental ones. The potential energy curves, transition dipole moments, spectroscopic parameters, and transition probabilities reported in this paper can be considered to be very reliable. The results obtained here can be used as guidelines for detecting these transitions, in particular those that have not been measured in previous experiments or have not been observed in the Sun, comets, stellar atmospheres, dark interstellar clouds, and diffuse interstellar clouds.