2Π Symmetry Research Articles

Reactive collisions between electrons and BeH+ above dissociation threshold.

Our previous studies of dissociative recombination and vibrational excitation/de-excitation of the BeH+ ion, based on the multichannel quantum defect theory, are extended to collision energies above the dissociation threshold, taking into account the vibrational continua of the BeH+ ion and, consequently, its dissociative excitation. We have also significantly increased the number of dissociative states of 2Π, 2Σ+ and 2Δ symmetry included in our cross section calculations, generating the most excited ones by using appropriate scaling laws. Our results are suitable for modeling the kinetics of BeH+ in edge fusion plasmas for collision energies up to 12 eV.

Spectroscopic Properties of the Alkali-Krypton Diatomic M-Kr (M = Rb, Cs, and Fr) van der Waals Systems Including the Spin-Orbit Coupling.

Using an ab initio approach based on pseudopotential technique, pair potential approach, core polarization potentials, and large Gaussian basis sets, we investigate interaction of heavy alkali-krypton diatomic M-Kr (M = Rb, Cs, and Fr) van der Waals dimers. In this context, the core-core interactions for M+-Kr (M = Rb, Cs, and Fr) are calculated at coupled-cluster single and double excitation (CCSD) level and included in the total potential energy. Therefore, the potential energy curves are performed for 14 electronic states: eight of 2Σ+ symmetry, four of 2Π symmetry, and two of 2Δ symmetry. Furthermore, for each M-Kr dimer, the spin-orbit coupling has been considered for the B2Σ+, A2Π, 32Σ+, 22Π, 52Σ+, 32Π, and 12Δ states. In addition, the transition dipole moment has been determined, including the spin-orbit effect using the rotational matrix issued from the spin-orbit potential energy calculations.

The 1.66 μm spectrum of the ethynyl radical, CCH

Frequency-modulated diode laser transient absorption spectra of the ethynyl radical have been recorded at wavelengths close to 1.66 μm. The observed spectrum includes strong, regular, line patterns. The two main bands observed originate in the ground X̃2Σ+ state and its first excited bending vibrational level of 2Π symmetry. The upper states, of 2Σ+ symmetry at 6055.6 cm−1 and 2Π symmetry at 6413.5 cm−1, respectively, had not previously been observed and the data were analyzed in terms of an effective Hamiltonian representing their rotational and fine structure levels to derive parameters which can be used to calculate rotational levels up to J = 37/2 for the 2Π level and J = 29/2 for the 2Σ one. Additionally, a weaker series of lines have been assigned to absorption from the second excited bending, (0 2 0), level of 2Σ symmetry, to a previously observed state of 2Π symmetry near 6819 cm−1. These strong absorption bands at convenient near-IR laser wavelengths will be useful for monitoring CCH radicals in chemical systems.

Structure and electronic properties of the doubly charged diatomic dications BeX2+ (X = Na, K)

The structural and electronic properties of the doubly charged diatomic dications BeX2+ (X = Na, K) have been systematically investigated. The ab initio calculations method is based on the use of non-empirical pseudopotentials for the Be2+, Na+, and K+ cores, Gaussian basis sets, and parameterized l-dependent polarization potentials. The potential energy curves and their spectroscopic properties for the low-lying electronic states of 2Σ+, 2Π, and 2Δ symmetries have been determined for the species BeNa2+ and BeK2+ for the first time. Results show, for each diatomic dication, that the ground and the first excited electronic states are repulsive. For both systems, for which no experimental and theoretical data are available, we discuss our results by comparing their potential energies with similar systems. Numerous avoided crossings between electronic states of 2Σ+ and 2Π symmetries have been localized and analyzed. Their existence is related to the interaction between the electronic states and to the charge transfer process between the two ionic structures Be(2+)X and Be(+)X(+). Furthermore, the transition dipole functions from the ground state to the 2-102Σ+ and between neighbor electronic states of 2Σ+ symmetry, revealed many abrupt changes, which are localized at particular distances corresponding to the positions of the avoided crossings.

Ab initio study of zinc chloride dication ZnCl2+ in the gas phase

Our high-level ab initio calculations show that the ZnCl2+ ground state of 2Π symmetry is metastable with a bond length of 2.242Å, an effective dissociation energy of 1.66eV, and an adiabatic double ionization energy of ZnCl of 26.11eV. Potential energy curves for 18 Λ+S states and ten Ω states of ZnCl2+ are presented as well as the associated spectroscopic constants. Tunneling lifetimes, spin–orbit induced predissociation lifetimes and radiative lifetimes for the vibrational levels in the low-lying electronic states of ZnCl2+ are determined and the metastability of the dication is discussed.

Theoretical study of LiK and LiK+ in adiabatic representation

The potential energy curves have been calculated for the electronic states of the molecule LiK within the range 3 to 300 a.u., of the internuclear distance R. Using an ab initio method, through a semiempirical spin-orbit pseudo-potential for the Li (1s2) and K (1s22s22p63s23p6) cores and core valence correlation correction added to the electrostatic Hamiltonian with Gaussian basis sets for both atoms. The core valence effects including core-polarization and core-valence correlation are taken into account by using an l-dependent core-polarization potential. The molecular orbitals have been derived from self-consistent field (SCF) calculation. The spectroscopic constants, dipole moments and vibrational levels of the lowest electronic states of the LiK molecule dissociating into K (4s, 4p, 5s, 3d, and 5p) + Li (2s, 2p, 3s, and 3p) in 1, 3Σ, 1, 3Π, and 1, 3Δ symmetries. Adiabatic results are also reported for 2Σ, 2Π, and 2Δ electronic states of the molecular ion LiK+ dissociating into Li (2s, 2p, 3s, and 3p) + K+ and Li+ + K (4s, 4p, 5s, 3d, and 5p). The comparison of the present results with those available in the literature shows a very good agreement in spectroscopic constants of some lowest states of the LiK and LiK+ molecules, especially with the available theoretical works. The existence of numerous avoided crossing between electronic states of 2Σ and 2Π symmetries is related to the charge transfer process between the two ionic systems Li+K and LiK+.

A comparative spectroscopic study of the excited electronic states of potassium-neon and potassium-helium systems

Configuration interaction studies have revealed the unexplored excited – state properties of potassium-neon and potassium-helium systems. In contrast to KHe, no potential barrier has been found in the lowest excited spin-orbit (12Π1/2) state of KNe. However, a small barrier of height 2 cm-1 and width 1.9 Ahave been predicted for the 12Π u,1/2state of the triatomic Ne-K-Ne system. Both spin-orbit components (12Π1/2, 3/2) of the diatomic and triatomic systems of potassium-neon are characterized by low binding energy values. Radiative lifetimes of these states are almost 10 ns lower than that of potassium-helium systems. Their high-lying excited states are having better binding energy values, especially, that of the triatomic ones, while huge barriers are only noticed in the high-energy 2Σ+ states. Stable exciplexes can be expected to form with respect to the two energetically similar excited states of 2Δ and 2Π symmetries. They are having radiative lifetimes of 25 ns and involved in important transitions to the 12Π state. This may eventually lead to the12Π -X2Σ+ emission near 13 330 cm-1 for KNe (12 900 cm-1 for Ne-K-Ne), which is on the lower wavelength side in comparison to potassium-helium systems. Their low-lying repulsive excited states can trigger the pumping of the blue-side and the red-side of the n s 2S1/2 → n p 2P3/2 transition, and this may ultimately give rise to the n p 2P1/2 → n s 2S1/2 lasing transition.

Theoretical study of the electronic structure of iridium monoxide

Potential energy curves of 25 low-lying electronic states of IrO are calculated with the multi-state complete active space second order perturbation theory (MS-CASPT2) method. The lowest state calculated without spin–orbit interactions has the 2Π symmetry. However, when spin–orbit coupling effect is considered, the ground state is the X4Δ7/2 and the 2Π3/2 is located 633 cm−1 above. The excited A2Δ state splits into A2Δ3/2 and A2Δ1/2, which are 8233 and 9741 cm−1 higher than the X4Δ2/7 state respectively. Electronic transitions from the two excited states H2ΔΩ and D2ΠΩ to the A2ΔΩ state produce the rotationally resolved bands observed experimentally.

Theoretical investigation of the low-lying electronic states of the alkaline hydride BeH2+ ion: Potential energy curves, spectroscopic constants, vibrational levels, and transition dipole functions

The structure and spectroscopic properties of the alkaline hydride BeH2+ ion have been investigated using an ab initio approach based on nonempirical pseudopotentials and parameterized l-dependent polarization potentials. The adiabatic potential energy curves and their spectroscopic constants for the ground and seventeen excited electronic states, dissociating into Be+(2s, 2p, 3s, 3p, 3d, 4s, 4p, and 4d) + H+ and Be2+ + H(1s and n = 2), of 2Σ+, 2Π, and 2Δ symmetries have been determined. As no experimental data are available, our results are discussed and compared with the few existing theoretical calculations. A very good agreement has been found with the previous theoretical data for the ground state; however many potential energy curves for the higher excited states are presented here, for the first time. Numerous avoided crossings between electronic states for 2Σ+ and 2Π symmetries have been localized and analyzed. Their existence is related to the interaction between the electronic states and to the charge transfer process between the two ionic systems Be2+H and Be+H+. In addition, we have calculated the vibrational energy level spacings of the bound electronic states. Furthermore, the adiabatic transition dipole functions from the X2Σ+ and 22Σ+ states to the higher excited states of 2Σ+ and 2Π symmetries have been evaluated and compared with the available theoretical work. This study represents the necessary initial step towards the investigation of the charge transfer processes in collision between Be+-H+ and Be2+-H.

One‐electron pseudopotential study of the alkali hydride cation NaH+: Structure, spectroscopy, transition dipole moments, and radiative lifetimes

AbstractThe structure and spectroscopic properties of the ground and the lowest excited electronic states of the alkali hydride cation NaH+ have been investigated using an ab initio approach. In this approach, a nonempirical pseudopotential for the Na+ core has been used and a core–core and a core‐valence correlation corrections have been added. The adiabatic potential energy curves and the molecular spectroscopic constants for numerous electronic states of 2Σ+, 2Π, and 2Δ symmetries, dissociating up to Na (4d) + H+ and Na+ + H (3d), have been calculated. As no experimental data are available, we discuss our results by comparing with the available theoretical calculations. A satisfying agreement has been found for the ground state with previous works. However, a clear disagreement between this study and the model potential work of Magnier (Magnier, J. Phys. Chem. A 2005, 109, 5411) has been observed for several excited states. Numerous avoided crossings between electronic states of 2Σ+ and 2Π symmetries have been found and analysed. They are related to the interaction between the potential energy curves and to the charge transfer process between the two ionic systems Na+H and NaH+. Furthermore, we provide an extensive set of data concerning the transition dipole moments from X2Σ+ and the 22Σ+ states to higher excited states of 2Σ+ and 2Π symmetries. Finally, the adiabatic potential energy curves of the ground (X2Σ+) and the first (22Σ+) excited states and the transition dipole moments between these states are used to evaluate the radiative lifetimes for the vibrational levels of the 22∑+ state for the first time. In addition to the bound–bound contribution, the bound‐free term has been evaluated and added to the total radiative lifetime. © 2012 Wiley Periodicals, Inc.

Theoretical study of low‐lying electronic states of the LiRb+ molecular ion: Structure, spectroscopy and transition dipole moments

AbstractThe electronic structure and the spectroscopic properties for low‐lying electronic states of the LiRb+ molecular ion, dissociating into Li (2s, 2p, 3s, 3p, 3d, 4s, and 4p) + Rb+ and Li+ + Rb (5s, 5p, 4d, 6s, 6p, 5d, and 7s), have been investigated using an ab initio approach based on non‐empirical pseudo potentials for the Li and Rb cores and parametrized l‐dependent polarization potential. We have determined the adiabatic potential energy curves and their spectroscopic constants for many electronic states of 2Σ+, 2Π, and 2Δ symmetries. A satisfying agreement, for the spectroscopic constants, has been obtained for the ground and the first excited states with the available theoretical works. Potential energy curves were presented, for the first time, for the higher excited states. In addition, we have localised and analysed the avoided crossings between electronic states of 2Σ+ and 2Π symmetries. Their existences can be related to the interaction between the potential energy curves and to the charge transfer process between the two ionic systems Li+Rb and LiRb+. Moreover, we have determined the transition dipole moments from X2Σ+ and 22Σ+ states to higher excited states of 2Σ+ and 2Π symmetries. For our best knowledge, no experimental data on the LiRb+ molecular ion is available. These theoretical data can help experimentalists to optimize photoassociative formation of ultracold LiRb+ molecular ion and their longevity in a trap or in an optical lattice. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

Electronic states of CsLi and CsLi+ molecules

Configuration interaction calculations have been carried out on electronic states of the CsLi molecule and the CsLi+ cation. Adiabatic potential energy, spectroscopic constants, dipole moments, and vibrational levels are presented for the lowest states of 1,3Σ+, 1,3Π, and 1,3Δ symmetries of the alkali dimer CsLi molecule dissociating into Cs (6s, 6p, 5d, 7s, and 7p) + Li (2s, 2p, 3s, 3p, and 3d) as well as for the lowest 2Σ+, 2Π, and 2Δ electronic states of the CsLi+ cation dissociating into Li (2s, 2p, 3s, 3p, and 3d) + Cs+ and Li+ + Cs (6s, 6p, 5d, 7s, and 7p). The results of the present many-electron configuration interaction calculations on the cation support the previous core-polarization effective potential calculations. The present calculations on the CsLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously. We have used an ab initio approach involving a nonempirical pseudopotential for the Li (1s2) and Cs cores and a core-valence correlation correction. A very good agreement of data from spectroscopic constants for some of the lowest states of the CsLi and CsLi+ molecules with those available in recent theoretical works has been obtained. The existence of numerous avoided crossings between electronic states of 2Σ+ and 2Π symmetries is related to a charge transfer process between the two ionic CsLi+ and LiCs+ systems.

Theoretical study of the electronic structure of LiNa and LiNa+ molecules

Adiabatic potential energy, spectroscopic constants, dipole moments, and vibrational levels of the lowest electronic states of the alkali dimer LiNa molecule dissociating into Na (3s, 3p, 4s, 3d, and 4p) + Li (2s, 2p, 3s, and 3p) in 1,3Σ, 1,3Π, and 1,3Δ symmetries are presented. Adiabatic results are also reported for 2Σ, 2Π, and 2Δ electronic states of the molecular ion LiNa+ dissociating into Li (2s, 2p, 3s, and 3p) + Na+ and Li+ + Na(3s, 3p, 4s, 3d, and 4p). We use an ab initio approach involving a non-empirical pseudopotential for the Li (1s2) and Na (1s22s22p6) cores and core valence correlation correction. A very good agreement is obtained for some lowest states of the LiNa and LiNa+ molecules for spectroscopic constants with the available theoretical works. The existence of numerous avoided crossings between electronic states of 2Σ and 2Π symmetries is related to the charge transfer process between the two ionic systems Li+Na and LiNa+.

Ab initio study of NaRb +: Potential energy curves, spectroscopic constants and atomic polarizabilities

Using an ab initio approach involving a non-empirical pseudopotentials for Na and Rb atoms, the adiabatic potential energy curves of 26 electronic states of NaRb + ionic molecule dissociating up to Na(4p) + Rb + and Na + + Rb(7s) have been investigated. Their molecular spectroscopic constants have been derived and compared with the available theoretical works. Furthermore, the transition dipole moments from X 2Σ + and 2 2Σ + to higher excited states have been determined. Numerous avoided crossings between electronic states of 2Σ + and 2Π symmetries have been localised and analysed. Their existences are related to the charge transfer process between the two ionic systems Na +Rb and NaRb +. The accurate potential energy curves have been exploited to realize a long-range vibrational level spacing analysis using the WKB semi-classical approximation in order to extract the Na and Rb atomic static dipole polarizabilities. A very good agreement between our static dipole polarizabilities and the available experimental and theoretical works has been observed.

Theoretical investigation on CsLi + and CsNa + ionic molecules

The potential energy curves and the spectroscopic constants of the ionic molecules CsLi + and CsNa + have been determined for the ground and the lowest 2Σ +, 2Π and 2Δ electronic states. Using an ab initio method, the calculation has been performed in a one active electron approach based on a non empirical pseudo-potentials with core valence effects taken into account through parameterized l-dependant polarization potentials. Numerous avoided crossing between electronic states of 2Σ + and 2Π symmetries have been localised and analysed for the both ionic molecules. Their existences are related to the charge transfer process between the two ionic systems Cs +X and CsX + (X = Li, Na). Furthermore, the transition dipole moment from the ground state X 2Σ + and the first excited state 2 2Σ + to higher excited states have been determined for both CsLi + and CsNa + ionic systems. For our best knowledge, there are neither experimental nor theoretical works realised on these ionic molecules.

Theoretical investigation of the molecular structure and transition dipole moments of the NaK + low lying electronic states

The electronic structure and the spectroscopic constants of the low lying electronic states of the NaK + ionic molecule have been determined through using an ab initio approach involving a non-empirical pseudopotential for the Na and K cores and core valence correlation correction. The potential energy of nearly 26 electronic states of 2Σ +, 2Π, and 2Δ symmetries has been calculated up to their dissociation limit Na(4 d) + K + and Na + + K(6 s). Their spectroscopic constants ( R e, D e, T e, ω e, ω e χ e, and B e) are derived and compared with the few available theoretical studies. A good agreement has been found for the ground state and few excited states with previous works. New potential energy curves were presented, for the first time, for the higher excited states. Numerous avoided crossing between electronic states of 2Σ +, 2Π symmetries have been localized and analyzed. Their existences are related to the charge transfer between the two ionic molecules Na +K and NaK +. Furthermore, we have determined the transition dipole moments for several states and analyzed the avoided crossings related to charge transfer between alkaline atoms.

Theoretical study of the electronic states and transition dipole moments of the LiK + molecule

The adiabatic potential energy, the spectroscopic constants and the transition dipole moments of the lowest electronic states of the LiK + molecule, dissociating into Li(2 s, 2 p, 3 s, 3 p, 3 d, 4 s, and 4 p) + K + and Li + + K(4 s, 4 p, 5 s, 3 d, 5 p, 4 d, and 6 s), have been investigated. We have used an ab initio approach involving a non-empirical pseudopotential for the Li (1 s 2) and K (1 s 22 s 22 p 63 s 23 p 6) cores and core valence correlation correction. A very good agreement has been obtained for the ground state for the spectroscopic constants with the available theoretical works. The transition dipole moment from X 2Σ, 2 2Σ, 3 2Σ, and 4 2Σ states to higher excited states have been determined. Numerous avoided crossing between electronic states of 2Σ and 2Π symmetries, have been localised and analysed. Their existences are related to the charge transfer process between the two ionic systems Li +K and LiK +.

Carbonyl Boron and Related Systems: An ab Initio Study of B−X and YB⋮BY (1Σg+), Where X = He, Ne, Ar, Kr, CO, CS, N2 and Y = Ar, Kr, CO, CS, N2

Using the coupled-cluster methodology and large correlation consistent basis sets, we have examined the BX and YBBY (1Σg+) molecules, where X = He, Ne, Ar, Kr, CO, CS, and N2 and Y = Ar, Kr, CO, CS, and N2. For the B−X series we have constructed full potential energy curves reporting total energies, equilibrium geometries, binding energies, and also spectroscopic constants for the diatomic sequence. The B−CO, B−CS, and B−N2 ground states are of 4Σ- and 2Π symmetries, respectively, with the 4Σ- states having remarkably strong binding energies with respect to their adiabatic fragments. For all the triatomics the first excited 4P state of B plays an instrumental role in the binding process, while the bonding mechanism in either the 2Π or 4Σ- symmetries is due to charge transfer to the empty 2pz orbital of the B atom. The YBBY series results by singlet coupling two B−Y 4Σ- moieties, leading to acetylene-like YB⋮BY systems of 1Σg+ symmetry.

Electronic states of HNO + and HON +

The three-dimensional CASSCF-MRCI potential energy functions have been calculated for the X 2 A ′ and A 2 A ″ electronic states of the HNO + and HON + isomers. In both cases, these two states form a bent-linear Renner–Teller pair in 2Π symmetry. The barriers to linearity of the X state are calculated to be 6846 cm −1 for HNO + and 8050 cm −1 for HON + (RCCSD(T)). Both isomers possess a conical intersection arising from the crossing between the first excited 2Σ + state and the X 2Π state along the collinear ( NO +( X 1Σ +)+ H( 2 S)) dissociation path. The barrier for isomerisation has been calculated to be 19457 cm −1 (MRCI) and the HNO + isomer is more stable than HON + by 5819 cm −1. The rovibronic levels in the HNO + Renner–Teller system have been calculated by a variational method taking into account the coupling of the rovibrational, electronic and electron spin angular momenta. Since for HON + the barrier to dissociation of the X 2 A ′ ground state is located below the barrier to linearity, only low lying vibrational levels have been calculated for this isomer.

Theoretical Investigation of Scandium Carbide, ScC

The electronic structure of the diatomic carbide ScC has been investigated by ab initio multireference methods in conjunction with large basis sets. The ground state has been determined to be of 2Π symmetry with De = 65.5 kcal/mol and Re = 1.988 Å. Eight more states have been examined within an energy range of about 1 eV, with the first excited state (4Π) being 1.2 kcal/mol higher.