Spectroscopic Constants Research Articles

Resonant Ionic, Covalent Bond, and Steric Characteristics Present in 1Σu+ States of Li2

The molecular bonding in the excited states of the alkali dimers involves the resonant ionic, covalent bond and steric interactions. We show here the case of the 1Σu+ states of Li2 by ab initio calculation. These interactions as functions of the internuclear distance lead to complex potential energy curves, providing an important application for high resolution laser spectroscopy. The spectroscopic constants for the 4 and 5 1Σu+ states are obtained for the first time.

Spectroscopic constants and anharmonic force field of dithioformic acid and its isomers: a theoretical study.

The potential astronomical interest dithioformic acid (trans-HC(= S)SH) exists five isomers and has received considerable attention of astronomical observation in recent years. The different positions of H atoms of five isomers lead to diverse point groups, dipole moments, and spectroscopic constants. The anharmonic force field and spectroscopic constants of them are calculated using CCSD(T) and B3LYP employing correlation consistent basis sets. Molecular structures, dipole moments, rotational constants, and fundamental frequencies of trans-HC(= S)SH are compared with the available experimental data. The B3LYP/Gen = 5 and CCSD(T)/Gen = Q results can reproduce them well. Molecular structures, dipole moments, relative energies, spectroscopic constants of cis-HC(= S)SH, and dithiohydroxy carbene (DTHC) are also calculated. The new data obtained in this study are expected to guide the future high resolution experimental work and to assist astronomical search for CH2S2.

Ab-initio study of the electronic structure of LaF including spin-orbit coupling.

Spectroscopic investigation of lanthanum monofluoride molecule LaF is carried out by ab-initio methods and all the observed band systems are predicted through the fine structure of LaH. This structure consisted of 67 Ω(±) states is calculated by taking into account the spin-orbit coupling effect of lanthanum. Therefore, these Ω(±) states are degenerated from 33 low-lying 1,3Λ(±) states below 33,200cm-1. The potential energy curves (PECs) of 1,3Λ(±) and Ω(±) states are displayed in the range of internuclear distance from 1.40 to 3.00Å and their spectroscopic constants ([Formula: see text],[Formula: see text], [Formula: see text], [Formula: see text]) are reported. Moreover, the permanent and the transition dipole moments are plotted as a function of internuclear distance. Furthermore, the composition of the Ω(±) state-wave functions in terms of Λ-S parent states is calculated at the equilibrium internuclear distance of the ground state. Furthermore, through calculating the splitting energy between the spin-orbit components of a 3Λ(±) state, Hund's case of many states involved in the observed band systems is determined.

Laser Cooling with an Intermediate State and Electronic Structure Studies of the Molecules CaCs and CaNa.

The ground and excited electronic states of the diatomic molecules CaCs and CaNa have been investigated by implementing the ab initio CASSCF/(MRCI + Q) calculation. The potential energy curves of the doublet and quartet electronic low energy states in the representation 2s+1Λ(±) have been determined for the two considered molecules, in addition to the spectroscopic constants Te, ωe, Be, Re, and the values of the dipole moment μe and the dissociation energy De. The determination of vibrational constants Ev, Bv, Dv, and the turning points Rmin and Rmax up to the vibrational level v = 100 was possible with the use of the canonical functions schemes. Additionally, the transition and the static dipole moments curves, Einstein coefficients, the spontaneous radiative lifetime, the emission oscillator strength, and the Franck–Condon factors are computed. These calculations showed that the molecule CaCs is a good candidate for Doppler laser cooling with an intermediate state. A “four laser” cooling scheme is presented, along with the values of Doppler limit temperature TD = 55.9 μK and the recoil temperature Tr = 132 nK. These results should provide a good reference for experimental spectroscopic and ultra-cold molecular physics studies.

Study of the 15N14N18O absorption bands in the 4200–6500 cm−1 region

Five bands of 15N14N18O nitrous oxide isotopologue were detected in the 4200–6500 cm−1 region with a Bruker IFS-125M Fourier transform spectrometer using a sample composed of NO (80% of 15N18O and 20% of 14N16O) and a trace amount of N2O isotopologues. The line positions of these bands were measured to the uncertainties of 0.001 cm−1. The spectroscopic constants were fitted using the measured line positions. The root mean squares of the residuals (RMS) of the fits (0.0005 cm−1 0.0027 cm−1) were close to the experimental uncertainties. Four bands, , and , were observed for the first time. The line positions of the 2 ν 3 band were determined with a smaller uncertainty than in (A. W. Mantz, K. Narahari Rao, L.H. Jones, R.M. Potter. J. Mol. Spectrosc. 30, 513 (1969)).

Bound state solutions and thermodynamic properties of modified exponential screened plus Yukawa potential

In this research paper, the approximate bound state solutions and thermodynamic properties of Schrӧdinger equation with modified exponential screened plus Yukawa potential (MESPYP) were obtained with the help Greene–Aldrich approximation to evaluate the centrifugal term. The Nikiforov–Uvarov (NU) method was used to obtain the analytical solutions. The numerical bound state solutions of five selected diatomic molecules, namely mercury hydride (HgH), zinc hydride (ZnH), cadmium hydride (CdH), hydrogen bromide (HBr) and hydrogen fluoride (HF) molecules were also obtained. We obtained the energy eigenvalues for these molecules using the resulting energy eigenequation and total unnormalized wave function expressed in terms of associated Jacobi polynomial. The resulting energy eigenequation was presented in a closed form and applied to study partition function (Z) and other thermodynamic properties of the system such as vibrational mean energy (U), vibrational specific heat capacity (C), vibrational entropy (S) and vibrational free energy (F). The numerical bound state solutions were obtained from the resulting energy eigenequation for some orbital angular quantum number. The results obtained from the thermodynamic properties are in excellent agreement with the existing literature. All numerical computations were carried out using spectroscopic constants of the selected diatomic molecules with the help of MATLAB 10.0 version. The numerical bound state solutions obtained increases with an increase in quantum state.

Relativistic calculations on the transition electric dipole moments and radiative lifetimes of the spin-forbidden transitions in the antimony hydride molecule

Calculations on the spectroscopic constants and transition properties of the first three states (a1Δ, b1Σ+, and X3Σ−) of the SbH molecule were performed under the relativistic framework using the exact two-component Hamiltonian (X2C). The potential energy curves in the Franck–Condon region were computed and compared with the previous values. Furthermore, the transition dipole moments for the weak spin-forbidden transitions (b0+–X10+, b0+–X21, X10+–X21, and X21–a2) were reported. The spontaneous radiative lifetime of the b1Σ+ (υ′ = 0) state was calculated as 163.5±7.5 μ s, which is in reasonable agreement with the latest experimental value of 173±3 μ s. The spontaneous radiative lifetimes of the X21 (υ′ = 0) state and the a2 (υ′ = 0) state were calculated to be 48.6 s and ∼ 8 ms, respectively. Our study is expected to be a benchmark transition property computation for comparison with other theoretical and experimental results. The datasets presented in this paper, including the transition dipole moments, are openly available at https://dx.doi.org/10.11922/sciencedb.j00113.00018.

Exact-Two-Component Relativistic Multireference Second-Order Perturbation Theory.

As the relativistic corrections become stronger for late-row elements, the fully perturbative treatment of spin-orbit coupling and dynamic correlation may become inadequate for accurate descriptions of chemical properties. In this work, we introduce a determinant-based Kramers-unrestricted exact-two-component multireference second-order perturbation (X2C-MRPT2) method which variationally includes relativistic corrections with a perturbative dynamic correlation. The restricted active space partitioning scheme is employed to provide an adjustable correlation space for the second-order perturbation treatment. The multistate perturbation theory is also developed to improve the descriptions of ground and excited states. Benchmark studies of atomic fine-structure splittings and spectroscopic constants of molecular monohydrides using X2C-MRPT2 are compared to the other perturbative and variational approaches. The results suggest that X2C-MRPT2 is a highly accurate alternative to the fully variational multireference configuration interaction method at only a small fraction of the computational cost.

Theoretical study on potential energy surface and bound states of the Kr-CNCN complex: Compared with the Kr-NCCN system

The first ab initio potential energy surface of the Kr-CNCN system is investigated using the single double excitation coupled-cluster theory with noniterative treatment of triple excitation. The mixed basis sets are used with aug-cc-pVTz for the C and N atoms and aug-cc-pVTz-pp for the Kr atom, including an additional midbond function of 3s3p2d1f1g. The computed single point energies at 585 configurations are fitted to an analytical potential model. The potential energy surface of the Kr-CNCN complex has a nearly T-shaped global minimum with the energy of −286.6 cm−1 located at R = 6.88 a0, θ = 89.3°. The interaction of the linear CNCNKr geometry is stronger than that of the linear KrCNCN structure. The whole potential energy surface of the Kr-CNCN presents angular anisotropy. The bound state energies up to J = 9 and the wave functions are calculated by analytically solving the Schrödinger equation based on the ab initio potential energy surface. The calculated fundamental frequencies of bending vibration and stretching vibration of the Kr-CNCN are 24.0 cm−1 and 32.7 cm−1, respectively. The transition frequencies and the spectroscopic constants of the Kr-CNCN system are predicted, and the relevant results are compared with the Kr-NCCN complex. The differences in the PES and bound state energy levels between the Kr-CNCN and Kr-NCCN complexes are clarified. These results will help to further explore the formation causes of CN radical in the interstellar medium and provide a theoretical basis for future experimental spectra research of the Kr-CNCN system.

Synthesis, Purification, and Rotational Spectroscopy of 1-Cyanocyclobutene (C5H5N)

The rotational spectrum of 1-cyanocyclobutene from 130 to 360 GHz has been observed, assigned, and least-squares fit for the ground state and the two lowest-energy vibrationally excited states. Synthesis by UV photochemical dimerization of acrylonitrile and subsequent base-catalyzed dehydrocyanation affords a highly pure sample, yielding several thousand observable rotational transitions for this small organic nitrile. Over 2500 a-type, R-branch transitions of the ground state have been least-squares fit to low error with partial-octic A- and S-reduced Hamiltonians, providing precise determinations of the corresponding spectroscopic constants. In both reductions, computed spectroscopic constants are in close agreement with their experimentally determined counterparts. Two vibrationally excited states (ν27 and ν17) form a Coriolis-coupled dyad, displaying many a-type and b-type local resonances and related nominal interstate transitions. Somewhat unexpectedly, despite the very small permanent b-axis dipole moment, a number of b-type transitions could be observed for the ν17 state; this is explained in terms of state mixing by the Coriolis perturbations. Over 2200 transitions for each of these states have been least-squares fit to a low-error, two-state, partial-octic, A-reduced Hamiltonian with nine Coriolis-coupling terms (Ga , GaJ, GaK, GaJJ, Fbc , FbcK, Gb , GbJ, and Fac). The availability of so many observed rotational transitions, including resonant transitions and nominal interstate transitions, enables a very accurate and precise determination of the energy difference (ΔE27,17 = 14.0588093 (43) cm-1) between ν27 and ν17. The spectroscopic constants presented herein provide a starting point for future astronomical searches for 1-cyanocyclobutene.

Theoretical study of the low-lying electronic states of diatomic antimony oxide including the spin-orbit coupling effect

In this paper, accurate determinations of electronic structures and spectroscopic features for the Λ−S and Ω low-lying electronic states of SbO are investigated by highly correlated ab initio calculations. Energies of twenty-four Λ−S states corresponding to the first two dissociation asymptotes, as well as the lowest twelve Ω states, are obtained and then used to construct their potential energy curves. Spectroscopic constants and vibrational states for all bound states are determined and are consistent with experimental data. The spin-orbit coupling effect has introduced a minor impact on the electronic states of SbO. Additional calculations for the low-lying electronic states of PO, AsO and BiO are also carried out to further verify the computational accuracy of SbO. Our derived results for these VA group oxides are in reasonable agreement with available experimental data. In addition, emission spectra of the excited Ω states to the ground one are simulated. The predictive results are anticipated to serve as guidelines for further research such as assisting laboratorial detections and analyzing the observed spectrum of SbO.

Rotational spectrum of anti- and gauche-4-cyano-1-butyne (C5H5N) – An open-chain isomer of pyridine

The analysis of the rotational spectrum of 4-cyano-1-butyne, an open-chain isomer of pyridine, is presented herein for the first time. Transitions for the ground vibrational states of both conformational isomers, anti and gauche, were observed in the 8–38 GHz and 130–360 GHz frequency ranges and fit to effective sextic distorted-rotor Hamiltonians with low uncertainty (σfit < 50 kHz), allowing for their potential detection by radioastronomy or in harsh reaction environments. The microwave region includes hyperfine-split transitions for both conformers, allowing for the experimental determination of the χaa, χbb, and χcc quadrupole coupling constants. In the millimeter-wave region, not every observable ground-state transition could be satisfactorily addressed by a single-state Hamiltonian due to Coriolis coupling with the low-energy vibrationally excited states. Thus, effective single-state fits of the ground states were obtained by including only Ka-series transitions without obviously perturbed energy levels. Importantly, the effective fit does include the most intense transitions throughout the observed frequency ranges. The predicted values (MP2/cc-pVTZ) are in close agreement with the experimental spectroscopic constants. These data provide a sufficient foundation for the identification of anti- and gauche-4-cyano-1-butyne in the interstellar medium by radioastronomy. The gauche conformer is estimated to lie 1.00 (5) kcal/mol higher in energy than the anti conformer, as determined using experimental transition intensities.

Spectroscopy on the electron-electric-dipole-moment–sensitive states of ThF+

An excellent candidate molecule for the measurement of the electron's electric dipole moment (eEDM) is thorium monofluoride (ThF$^+$) because the eEDM-sensitive state, $^3\Delta_1$, is the electronic ground state, and thus is immune to decoherence from spontaneous decay. We perform spectroscopy on $X\,^3\Delta_1$ to extract three spectroscopic constants crucial to the eEDM experiment: the hyperfine coupling constant, the molecular frame electric dipole moment, and the magnetic $g$-factor. To understand the impact of thermal blackbody radiation on the vibrational ground state, we study the lifetime of the first excited vibrational manifold of $X\,^3\Delta_1$. We perform ab initio calculations, compare them to our results, and discuss prospects for using ThF$^+$ in a new eEDM experiment at JILA.

Configuration interaction study on excited electronic states and radiative lifetimes of SnI including spin-orbit coupling

In this work, the high-level multireference configuration interaction (MRCI) method is used to accurately calculate the electronic structure of SnI. In order to guarantee the computational precision, the Davidson correction (+Q), core-valence (CV) electrons correlations and spin-orbit coupling (SOC) effect are also considered. According to the calculated potential energy curves (PECs) of the Λ-S states and Ω states, the spectroscopic constants of the bound states are estimated. The interaction of crossing states are investigated, and with the aid of calculated SO matrix elements, the predissociation pathways of 14Σ− state are revealed. In addition, the transition dipole moments (TDMs) and Franck-Condon factors (FCFs) from the excited states to the ground state are determined. Finally, the radiative lifetimes of bound states are calculated, and the influences of SOC effect on radiative lifetimes are illuminated.

Visible Opacity of M Dwarfs and Hot Jupiters: The TiO B 3Π−X 3Δ Band System

Abstract The TiO B 3Π − X 3Δ electronic transition ( γ ′ system) is an important opacity source in the atmospheres of M dwarfs and hot Jupiter exoplanets. The 0–0, 1–0, and 2–1 bands of the B 3Π − X 3Δ band system have been analyzed using a TiO emission spectrum recorded at the McMath-Pierce Solar Telescope, operated by the National Solar Observatory at Kitt Peak, Arizona. Improved spectroscopic and equilibrium constants were determined. Line strengths were calculated from an ab initio transition-dipole moment function scaled using an experimental lifetime. A new line list for v ′ = 0 – 2 and v″ = 0–4 of the B 3Π − X 3Δ band system is provided.

High resolution laser excitation spectra and Franck-Condon factors of A2Π−X2Σ+ electronic transition of MgF

Magnesium monofluoride (MgF) is proposed as an ideal candidate radical for direct laser cooling. Here, the rotationally resolved laser spectra of MgF for the A2Π−X2Σ+ electronic transition system were recorded by using laser induced fluorescence technique. The MgF radicals were produced by discharging SF6/Ar gas mixtures between the tips of two magnesium needles in a supersonic jet expansion. We recorded a total of 19 vibrational bands belonging to three sequences of Δv=0, ±1 in the region of 348-370 nm. Accurate spectroscopic constants for both X2Σ+ and A2Π states are determined from rotational analysis of the experimental spectra. Spectroscopic parameters, including the Franck-Condon factors (FCFs), are determined from the experimental results and the Rydberg-Klein-Rees (RKR) calculations. Significant discrepancies between the experimentally measured and RKR-calculated FCFs are found, indicating that the FCFs are nearly independent of the spin-orbit coupling in the A2Π state. Potential energy curves (PECs) and FCFs determined here provide necessary data for the theoretical simulation of the laser-cooling scheme of MgF.

Theoretical study of laser cooling of the BO+ molecular ion

The feasibility of laser-cooling BO+ cation is investigated by using the high-level ab initio calculation method. The potential energy curves (PECs) of the 24 Λ-S states are studied by the multi-reference configuration interaction (MRCI) method. The calculated spectroscopic constants of bound states of BO+ are in good agreement with available experimental and theoretical results. The dipole moments (DMs) of the BO+ ion are obtained and the transition dipole moments (TDMs) of 21Σ+-X1Σ+, 31Σ+-X1Σ+, 11Π-X1Σ+, 21Π-X1Σ+, 31Π-X1Σ+ and 21Π-11Π are calculated. Based on the computed PECs, the Franck-Condon factors (FCFs) of the 21Σ+-X1Σ+ transition are found to be highly diagonal. The radiative lifetime of the 21Σ+-X1Σ+ transition is calculated to be 36.73 ns, which is sufficiently short for laser cooling. The Einstein coefficient A and branching ratio R are evaluated, and the possibility of laser-cooling BO+ cation is discussed.

Spectroscopic Properties and Spin–Orbit Coupling of Electronic Excited States of GeCl+

The electronic structure and spectroscopic properties of GeCl+ are studied by high-level ab initio calculations by considering spin-orbit coupling (SOC). The potential energy curves (PECs) and spectroscopic constants of 12 Λ-S states and 23 Ω states are calculated using the multi-reference configuration interaction plus Davidson correction method (MRCI + Q), which are in good agreement with the experiment. Based on the calculated SO matrix and the PECs of the Ω states, the interaction between the d3Π state and other states caused by the SOC and the double-potential well structure caused by the avoided crossing rule and the properties of transitions d3Π0+-X1Σ+0+, d3Π1-X1Σ+0+, and a3Σ+1-X1Σ+0+ are studied. Our results indicate that the previously observed spectra of GeCl+ in the 290-325 nm range should be assigned as the a3Σ+1-X1Σ+0+ transition. Moreover, the predissociation behavior of the d3Π state between the vibrational levels v' = 1 and v' = 10 is discussed, and the radiative lifetimes of transitions d3Π0+-X1Σ+0+ and d3Π1-X1Σ+0+ are evaluated on the order of microseconds, while a3Σ+1-X1Σ+0+ is on the order of milliseconds. We estimate that the strongest bands of a3Σ+1-X1Σ+0+ are the 0-16, 0-17, and 0-18 bands. This study will promote our understanding of the detailed electronic structure and spectra of the GeCl+ radical cation.

Ab initio investigation of the ground and excited states of TcO+ and RhO+

High-level quantum calculations are utilized to analyze nineteen and thirteen lowest energy electronic states of TcO+ and RhO+. Their potential energy curves, equilibrium bond lengths, electronic excitation energies, harmonic vibrational frequencies, and anharmonicities are reported using quadruple-ζ and quintuple-ζ quality correlation consistent basis sets. The core electron correlation effects and equilibrium chemical bonding patterns of several low-energy electronic states are also considered. The ground state of TcO+ (11Ʃ+) (1σ21π41δ4) is triple bonded in nature, results adiabatically from the high energy Tc+(3P) + O(3P) fragments, and relates to the first excited state of TcO (2Σ+) (1σ22σ11π41δ4). The chemical bonding of TcO+(11Ʃ+) is identical to its isoelectronic RuO2+ (X1Ʃ+) ground state. The ground state of RhO+ (3Σ−) features a 1σ21π41δ42π2 electronic configuration. Moving from TcO+ to RhO+ the binding energy decreases by ∼15−20 kcal/mol, the metal-oxygen bond shortens by 0.07 Å, and the harmonic stretching frequency decreases by ∼170 cm−1. Bonding patterns and spectroscopic constants are compared for the neighboring species of RhO+ and TcO+.

Theoretical study of potential energy curves and vibrational levels of low-lying electronic states of SbS

In this paper, highly correlated &lt;i&gt;ab initio&lt;/i&gt; calculations are performed for accurately determining the electronic structures and spectroscopic features of the Λ-S and Ω low-lying electronic states of SbS . The potential energy curves for 27 Λ-S states of the first three dissociation asymptotes are constructed. Spectroscopic constants and vibrational states for all bound states are well determined. The calculated atomic states for both atoms are consistent with experimental data quite well. Several low-lying Ω electronic states are also investigated, and their respective spectroscopic constants and vibrational states are obtained and compared with those of corresponding Λ-S states, which indicates that the spin-orbit coupling effect gives rise to a minor influence on the electronic states of SbS. To verify our computational accuracy, the additional calculations for the low-lying electronic states of PS, AsS and BiS are also carried out. Our derived results are in reasonable agreement with available experimental data. In addition, vibrational spectra from the excited Ω states to the ground state of SbS are simulated, including bands of X(3/2)→X(1/2), 2(1/2)→X(1/2), 4(1/2)→X(1/2), 5(1/2)→X(1/2) and 6(1/2)→X(1/2). The X(3/2)→X(1/2) band is found in the mid-infrared region, while the others are located in the visible region. The predictive results provided in this paper are expected to serve as a guideline for further researches, such as assisting laboratorial detections and analyzing observed spectrum of SbS.