Vibronic Energy Levels Research Articles

Theoretical study of infrared and ultraviolet spectroscopy in SiP interstellar molecules

ABSTRACT Insufficient theoretical investigation is being conducted on the spectroscopic characteristics within the infrared wavelength range of SiP, an identified interstellar molecule. Using the ic-MRCI method, potential energy functions and dipole moment functions for the ground state (${X^2}\Pi $) and low excited states (${{\rm{A}}^2}{\Sigma ^ + }$) of the SiP molecule were calculated. Based on experimental spectroscopy data, least squares fitting was used for the potential energy functions of the ${X^2}\Pi $ and ${{\rm{A}}^2}{\Sigma ^ + }$ states. By combining these potential energy and dipole moment functions, the one-dimensional Schrödinger equation was solved to obtain the vibronic energy levels and Einstein A coefficients for the electronic states. Partition functions of the SiP molecule from 0.1 to 3000 K and the radiative properties of ${X^2}\Pi \leftrightarrow {X^2}\Pi $ and ${X^{\rm{2}}}\Pi \leftrightarrow {{\rm{A}}^2}{\Sigma ^ + }$ were derived. Infrared spectroscopy of the ${X^2}\Pi $ state and ultraviolet spectroscopy of the ${X^{\rm{2}}}\Pi \leftrightarrow {{\rm{A}}^2}{\Sigma ^ + }$ transition at 100 K, a temperature crucial for astronomical research, were calculated. Results indicate that the spectral-line intensity of the ${X^{\rm{2}}}\Pi \leftrightarrow {{\rm{A}}^2}{\Sigma ^ + }$ transition is greater, making it more suitable for astronomical observation. The obtained computational results in this paper yield spectroscopic parameters for the characterization of the interstellar molecule SiP, furnishing theoretical underpinnings for subsequent experimental observations.

How Does Pseudo-Jahn-Teller Effect Induce the Photoprotective Potential of Curcumin?

In this paper, the molecular and electronic structure of curcumin is studied. High-symmetric gas-phase tautomers and their deprotonated forms in various symmetry groups are identified. The stability of lower-symmetry structures was explained by using the Pseudo-Jahn-Teller (PJT) effect. This effect leads to stable structures of different symmetries for the neutral enol and keto forms. The presented analysis demonstrated the potential significance of the PJT effect, which may modulate the setting of electronic and vibrational (vibronic) energy levels upon photodynamic processes. The PJT effect may rationalize the photoprotection action and activity of naturally occurring symmetric dyes.

Quantum model of dynamic Stark‐induced degenerate vibronic state by two nonresonant shift‐up lasers for π‐electron angular momentum generation

AbstractA theoretical scenario for the generation of coherent π‐electron angular momentum in a low‐symmetry aromatic molecule using two nonresonant shift‐up lasers is presented. The effects of vibrational modes on coherent π‐electron angular momentum are considered in the adiabatic approximation. In this scenario, two electronic excited states are irradiated with two linearly polarized nonresonant lasers. This causes a consistent up‐shift in the vibronic energy levels of each electronically excited state toward higher energy as a result of the dynamic Stark effect. For the weak coupling case of the electronic‐vibrational interactions, the lowest vibronic states in the two electronic excited states are designed to be degenerate by varying the parameters (frequency and intensity) of each laser. The resultant degenerate state, called the dynamic Stark‐induced degenerate vibronic state (DSIDVS), is the origin of the coherent π‐electron angular momentum generation. An optimal laser parameter set is determined under conditions in which the lowest two vibronic states form the DSIDVS. The DSIDVS was formulated by the method of Laplace transformations. An analytical expression for the coherent π‐electron angular momentum was derived in the displaced harmonic oscillator model. We examined the dependence of the time‐averaged z‐component of the coherent angular momentum on the ratio of the two detunings and potential displacements of toluene, a typical low‐symmetry aromatic ring molecule, which belongs to the weak coupling case and is adopted to demonstrate the theoretical scenario. The inclusion of potential displacements in the angular momentum generation was found to reduce the value of by half, compared with that in the frozen nuclear approximation.

Electronic spectroscopy of the A1̃2A′′/A2̃2A′−X̃2A′ transitions of jet-cooled calcium ethoxide radicals: Vibronic structure of alkaline earth monoalkoxide radicals of C s symmetry

Laser-induced fluorescence/dispersed fluorescence (LIF/DF) and cavity ring-down spectra of the A1̃2A''/A2̃2A'-X̃2A' electronic transition of the calcium ethoxide (CaOC2H5) radical have been obtained under jet-cooled conditions. An essentially constant Ã2-Ã1 energy separation for different vibronic levels is observed in the LIF spectrum, which is attributed to both the spin-orbit (SO) interaction and non-relativistic effects. Electronic transition energies, vibrational frequencies, and spin-vibrational eigenfunctions calculated using the coupled-cluster method, along with results from previous complete active space self-consistent field calculations, have been used to predict the vibronic energy level structure and simulate the recorded LIF/DF spectra. Although the vibrational frequencies and Franck-Condon (FC) factors calculated under the Born-Oppenheimer approximation and the harmonic oscillator approximation reproduce the dominant spectral features well, the inclusion of the pseudo-Jahn-Teller (pJT) and SO interactions, especially those between the A1̃2A″/A2̃2A' and the B̃2A' states, induces additional vibronic transitions and significantly improves the accuracy of the spectral simulations. Notably, the spin-vibronic interactions couple vibronic levels and alter transition intensities. The calculated FC matrix for the A1̃2A''/A2̃2A'-X̃2A' transition contains a number of off-diagonal matrix elements that connect the vibrational ground levels to the levels of the ν8 (CO stretch), ν11 (OCC bending), ν12 (CaO stretch), ν13 (in-plane CaOC bending), and ν21 (out-of-plane CaOC bending) modes, which are used for vibrational assignments. Transitions to the ν21(a″) levels are allowed due to the pJT effect. Furthermore, when LIF transitions to the Ã-state levels of the CaOC-bending modes, ν13 and ν21, are pumped, A1̃2A''/A2̃2A'→X̃2A' transitions to the combination levels of these two modes with the ν8, ν11, and ν12 modes are also observed in the DF spectra due to the Duschinsky mixing. Implications of the present spectroscopic investigation to laser cooling of asymmetric-top molecules are discussed.

Electronic band structure of phosphorus-doped single crystal diamond: Dynamic Jahn-Teller distortion of the tetrahedral donor ground state

The electronic band structure of the phosphorus-doped high-quality high-pressure and high-temperature--grown single crystal diamond was studied by infrared absorption, magneto- and electron paramagnetic resonance spectroscopy, and first-principles calculations. The complete picture of the $1s\ensuremath{\rightarrow}n{p}_{\ifmmode\pm\else\textpm\fi{}}$ and $1s\ensuremath{\rightarrow}n{p}_{0}$ ($n=2$, 3, 4) donor transitions with new $1s\ensuremath{\rightarrow}3p{}_{0},4p{}_{0}$ and $1s\ensuremath{\rightarrow}4p{}_{\ifmmode\pm\else\textpm\fi{}}$ transitions allowed us to refine the energy levels of ground and exited states with those obtained from effective mass approximation calculation. For the first time, as far as we know, we have observed the fine doublet structures of the $1s$(${\mathrm{B}}_{2},\mathrm{E})\ensuremath{\rightarrow}2{p}_{\ifmmode\pm\else\textpm\fi{}}, 1s$(${\mathrm{B}}_{2},\mathrm{E})\ensuremath{\rightarrow}4p{}_{0}, 1s$(${\mathrm{B}}_{2},\mathrm{E})\ensuremath{\rightarrow}3p{}_{\ifmmode\pm\else\textpm\fi{}}$, and $1s$(${\mathrm{B}}_{2},\mathrm{E})\ensuremath{\rightarrow}4p{}_{\ifmmode\pm\else\textpm\fi{}}$ donor transitions with the splitting value of 1.05 meV. These doublet structures arise from the dynamic Jahn-Teller (JT) distortion which splits the energy level of the $1s$(${\mathrm{T}}_{2}$) state in the ${\mathrm{T}}_{d}$ configuration into those of the $1s$(${\mathrm{B}}_{2}$) ground state and the $1s$(E) state in the ${\mathrm{D}}_{2d}$ configuration. The dynamic JT distortion of the tetrahedral donor ground state has been proved by following facts: the observation of vibronic energy levels and temperature behavior of doublet bands in the IR spectrum, the absence of P-donor-related electron paramagnetic resonance signals, and first-principles calculations. We believe that the dramatic broadening of the $2p{}_{0}$ band attributed to the $1s$(${\mathrm{B}}_{2},\mathrm{E})\ensuremath{\rightarrow}2{p}_{0}$ donor transition at 524 meV is caused by the resonant interaction of this 524 meV energy level with that of \ensuremath{\sim}517 meV formed due to the dynamic JT coupling of the $1s$(E) energy level equal to 387 meV with the longitudinal acoustic phonon of $\ensuremath{\sim}130$ meV.

Electronic spectrum of boron dichloride. theoretical study of vibronic levels of the ground and first excited states

As expected by the Walsh diagram of AB2 molecules, the electronic spectrum of BCl2 radical involves bent-linear transitions between the ground and first excited states that form the two degenerate components of the 2Π electronic state of the linear molecule. A high level ab-initio theoretical study on BCl2 radical has been undertaken by constructing potential energy surfaces (PES) using the coupled-cluster singles and doubles with perturbative triples (CCSD(T)) with aug-cc-pVQZ for boron and aug-cc-pV(Q + d)Z for chlorine atoms. Vibronic energy levels were determined variationally, from the obtained PES, up to ~35,000 cm−1 above the relative minima of the ground and excited states. Low-lying vibrational levels of the ground and first excited electronic states were obtained, which showed a very complex structure which is known to be as a result of large Renner-Teller vibronic coupling. For the most abundant isotopologue, 11B35Cl2, the ground state fundamental frequencies are; ω10= 696.0 cm−1, ω20= 281.0 cm−1 and ω30=981.8 cm−1. For the same isotopologue, vibrational fundamentals of the excited state were estimated by fitting Σ vibronic levels to be ω10= 463.2 cm−1, ω20= 281.7 cm−1 and ω30=1245.1 cm−1.

Ab initio investigation of dicyanoacetylene cation in the ground electronic state: Vibronic coupling and photoionization selection rules

Dicyanoacetylene cation, C4N2+, is a species of astrochemical interest. The vibronic spectrum of the ground electronic state of the C4N2+ (X2Πu) is affected by a combination of the Renner–Teller and spin-orbit coupling. The first theoretical prediction of the vibronic energy levels in the ground electronic state of C4N2+ was carried out in 2011 (Ranković et al., 2011). Recently, Lamarre et al. (2015) reported the vibronic spectrum of this species obtained by the PFI-ZEKE photoelectron spectroscopy. They reported discrepancies between the experimental results and the previous theoretical predictions. In the present work, those discrepancies were resolved by using Renner-Teller parameters obtained by the explicitly correlated coupled-cluster method, CCSD(T)-F12, which includes dynamical correlation to a sufficient extent. Using these parameters, the vibronic spectrum was calculated in a variational manner. Reassignment of two experimentally observed vibronic levels is proposed and agreement between the calculated and experimentally observed levels was achieved. Furthermore, the photoionization selection rules were applied to the X+2Πu←X1Σg+ transition with the aim to elucidate more details about this process.

Branching Ratios, Radiative Lifetimes, and Transition Dipole Moments for YbOH.

Medium resolution (Δν̃ ∼ 3 GHz) laser-induced fluorescence (LIF) excitation spectra of a rotationally cold sample of YbOH in the 17300-17950 cm-1 range have been recorded using two-dimensional (excitation and dispersed fluorescence) spectroscopy. High resolution (Δλ ∼ 0.65 nm) dispersed laser-induced fluorescence (DLIF) spectra and radiative decay curves of numerous bands detected in the medium resolution LIF excitation spectra were recorded. The vibronic energy levels of the X̃2Σ+ state were predicted using a discrete variable representation approach and compared with observations. The radiative decay curves were analyzed to produce fluorescence lifetimes. DLIF spectra resulting from high resolution (Δν̃ < 10 MHz) LIF excitation of individual low-rotational lines in the Ã2Π1/2(0,0,0)-X̃2Σ+(0,0,0), Ã2Π1/2(1,0,0)-X̃2Σ+(0,0,0), and [17.73]Ω = 0.5(0,0,0)-X̃2Σ+(0,0,0) bands were also recorded. The DLIF spectra were analyzed to determine branching ratios which were combined with radiative lifetimes to obtain transition dipole moments. The implications for laser cooling and trapping of YbOH are discussed.

Jahn-Teller effect problems via ultrasonic experiments. Application to the impurity crystal CdSe:Cr

Based on the data analysis of ultrasonic experiments, a novel approach has been developed to explore Jahn-Teller effect (JTE) problems in non-cubic crystals with JT centers without involving additional experimental data beyond the information about the electronic term and crystal symmetry. Distinguished from cubic crystals, the axis of symmetry of the bulk non-cubic crystal do not necessarily coincide with those of the local impurity center, thus complicating the relation between the distortions produced by the ultrasound wave and the JTE active modes. We analysed the problem with corresponding calculations for the wurtzite-type hexagonal crystal CdSe:Cr2+, in which the chromium ion substitutes the cadmium one in the tetrahedral environment, resulting in its electronic ground state 5 T 2(e2t2 ). Experimental investigation of this system by ultrasound at frequencies of 28-105 MHz in the temperature range of 4-180 K, yields a peak in the attenuation of the ultrasound below 40 K for the normal modes related to the c 11, c 44, c 55, c 55, and c 66 elastic moduli. The peak has been interpreted as the manifestation of the JTE, similar to the one, observed in cubic crystals doped with 3d ions. However, no anomalies of attenuation have been detected for the mode related to the c 33 elastic modulus, in contradiction to the theoretical predictions based on the previous method, worked out for cubic crystals. In the new method we obtained direct relations between the deformations, related to the crystal moduli, and the local JT modes, calculated the partition functions for each of the three possible JTE problems for systems with an electronic T term, T⊗e, T⊗t2 and T⊗(e + t2) revealed how these deformations alter the vibronic energy levels responsible for the relaxations in the JT centers. It emerged that in the wurtzite crystal under consideration, only in the T⊗e problem the deformation related to the elastic moduli c 33 displaces all the vibronic energy level uniformly, without relaxation possibilities, thus supporting the new method and explaining the experimental observations.

Electric Field Control of the Valence‐Tautomeric Transformation in Cobalt Complexes

In this work a single valence‐tautomeric cobalt complex placed in a dc electric field has been examined. Along with the interaction with the electric field, the model employed accounts for intramolecular transfer of the excess electron as well as vibronic and exchange interactions. To obtain the energy spectrum of the valence‐tautomeric complex in the electric field, the vibronic problem of the pseudo‐Jahn–Teller effect has been solved. The vibronic (hybrid) wave functions and energy levels were used to calculate the temperature and field dependence of the molecular magnetic moment, as well as the polarization and shape of the absorption band in the near‐IR range, which is related to the light‐induced transfer of the electron from the catecholate ligand to the metal ion. It is predicted that the application of a dc electric field leads to electric polarization and a significant change in the magnetic and spectroscopic properties. The unique possibility of controlling electrically the magnetic state and optical and polarization characteristics of a valence‐tautomeric molecule is predicted.

Three-Dimensional Diabatic Potential Energy Surfaces for the Photodissociation of Thiophenol.

New reduced three-dimensional (3D) diabatic potential energy surfaces (PESs) involving the 1ππ, 1ππ*, and 1πσ* states for the nonadiabatic photodissociation C6H5SH(S0) + hv → C6H5SH(1ππ*/1πσ*) → H + C6H5S•(A/X) were constructed at a high computational level, namely explicitly correlated multireference configuration interaction (MRCI-F12) method with the cc-pVTZ-F12 basis. The diabatization of the PESs was achieved by a simple, efficient, and reliable "regularized diabatization" method [Köppel, H.; Gronki, J.; Mahapatra, S. J. Chem. Phys. 2001, 115, 2377-2388]. The dissociation energy of the S0 state and the excitation energies of the excited S1 and S2 states were found to be in reasonably good agreement with the experimental values. The vibronic energy levels of the thiophenol (PhSH) and deuterated thiophenol (PhSD) for S0 and S1 states were calculated using a three-dimensional model, and they are in reasonably good agreement with the available experimental results, which validate the high accuracy of the adiabatic PESs and the reasonability of the diabatic couplings.

On the Jahn–Teller effect in the [formula omitted] electronic ground state of CH3F+

In view of recent experimental and theoretical developments, we revisit our earlier theoretical studies (Mahapatra et al., 2004, 2005) on the Jahn–Teller effect in the degenerate X∼2E electronic ground state of CH3F+. The electronic potential energy surfaces and the coupling surfaces are re-calculated employing state-of-the-art ab initio quantum chemistry methods. The vibronic Hamiltonian, constructed with the aid of multimode vibronic coupling theory and symmetry selection rules, is systematically extended to higher order in the Taylor series expansion and the parameters are carefully revised in the present study. First principles quantum dynamics study is carried out to calculate the vibronic eigenvalue spectrum of this degenerate electronic state of CH3F+. The vibronic energy levels are assigned and compared with the experimental pulsed-field-ionization zero-electron-kinetic energy (PFI-ZEKE) and one photon ZEKE spectra of CH3F+ and also with the earlier theoretical results reported in the literature.

Spin Switching in Molecular Quantum Cellular Automata Based on Mixed-Valence Tetrameric Units

In this article we focus on the study of spin effects in a single square-planar mixed-valence cell comprising two electrons and in coupled molecular cells for quantum cellular automata. Using the vibronic model we demonstrate that the polarizabilities of the cell are different in spin-singlet and spin-triplet states of the electronic pair. Based on this inference the concept of spin switching in molecular quantum cellular automata is proposed, and the conditions under which this effect is feasible are derived. In order to reveal these conditions we have performed a series of quantum-mechanical calculations of the vibronic energy levels of the isolated cell and of the cell subjected to the external polarizing field. To present the results in a descriptive way they are qualitatively discussed in terms of the adiabatic potential curves illustrating spin effects in switching cycle during operation in quantum cellular automata. The spin-switching effect stemming from the theoretical model is shown to be depend...

Electric Field Control of Spin-Dependent Dissipative Electron Transfer Dynamics in Mixed-Valence Molecules

We demonstrate that the borderline class II/III magnetic MV dimers, which can be referred to as single molecule multiferroics, provide a unique possibility to achieve electric field control of the electron transfer (ET) dynamics. As an example, we consider a MV dimer d2-d1 in which an extra electron is delocalized over two spin-cores (s0 = 1/2), and the ET is spin-dependent due to the double exchange mechanism. It is assumed that the “extra” electron is coupled to the only intramolecular vibration, and a weak coupling to the dissipative subsystem (thermal bath) is taken into account. The vibronic energy levels and the wave functions of the isolated dimer (quantum part of the system) are numerically evaluated within the vibronic Piepho, Krausz, and Schatz (PKS) model. The dissipative dynamical behavior is treated within the multilevel Redfield approach for the reduced density matrix. The external electric field is assumed to initially stabilize either ferro (S = 3/2)- or antiferromagnetic (S = 1/2) spin st...

An experimental and theoretical study of the electronic spectrum of the HBCl free radical.

Following our previous discovery of the spectra of the HBX (X = F, Cl, and Br) free radicals [S.-G. He, F. X. Sunahori, and D. J. Clouthier, J. Am. Chem. Soc. 127, 10814 (2005)], the Ã(2)A(″)Π-X̃(2)A(') band systems of the HBCl and DBCl free radicals have been studied in detail. The radicals have been prepared in a pulsed electric discharge jet using a precursor mixture of BCl3 and H2 or D2 in high pressure argon. Laser-induced fluorescence (LIF) and single vibronic level emission spectra have been recorded to map out the ground and excited state vibrational energy levels. The band system involves a linear-bent transition between the two Renner-Teller components of what would be a (2)Π electronic state at linearity. We have used high level ab initio theory to calculate the ground and excited state potential energy surfaces and have determined the vibronic energy levels variationally. The theory results were used to assign the LIF spectra which involve transitions from the ground state zero-point level to high vibrational levels of the excited state. The correspondence between theory and experiment, including the transition frequencies, upper state band symmetries, and H, B, and Cl isotope shifts, was used to validate the assignments.

Tunneling splittings in vibronic energy levels of [formula omitted] studied by high resolution photoelectron spectroscopy and ab initio calculation

The energy levels of CD3F+(X∼2E) have been measured up to 1400cm−1 above the ground vibrational state using the one-photon zero-kinetic energy photoelectron (ZEKE) spectroscopic method. The spin-vibronic energy levels have also been calculated using an ab initio diabatic model. The potential energy surfaces of CD3F+ were calculated from those of CH3F+ using a transformation of the normal coordinates. The calculations show that tunneling splittings of vibrational energy levels exist due to the three equivalent wells caused by the linear-plus-strong quadratic Jahn–Teller coupling. The splittings are smaller than those in CH3F+. The experimental spectrum was assigned based on the fundamental vibrational modes calculated at the energy minimum. The calculated spin-vibronic energy levels are in good agreement with the experimental data. The tunneling splitting pairs for the fundamental vibrations related to the CD3 rock were observed. The first adiabatic ionization energy was determined as 101534±3cm−1 or 12.5886±0.0004eV.

Theoretical Investigations on CaO Ions: Vibronic States and Photoelectron Spectroscopy

The low-lying electronic states, X(2)Π and A(2)Σ(+) of CaO(+) and X(2)Σ(+) and A(2)Π of CaO(-), have been determined at the MRCI+Q level of theory with the aug-cc-pV5Z(O) and cc-pCV5Z(Ca) basis sets. The two states of CaO(+) are close within <0.1 eV and coupled via spin-orbit effect. The X(2)Σ(+) and A(2)Π states of CaO(-) are energetically separated by <1 eV such that the first excited state is close to the electronic ground state of neutral CaO and unstable with respect to electron detachment. Using the potential energy curves and the spin-orbit coupling terms, the vibronic energy levels of these ions have been determined. The ionization energy and the electron affinity of CaO are calculated at 6.79 and 0.79 eV, respectively. The photoelectron spectra of CaO(-) and CaO have also been simulated.

Jahn–Teller Effect in VCl4

A theoretical study is made of the Jahn-Teller and other properties of vanadium tetrachloride. Relativistic effective core potentials and corresponding valence spin-orbit operators are used with Gaussian atomic orbitals to compute self-consistent-field and spin-orbit configuration-interaction wave functions. Energy-surface parameters, electronic excitation energies, vibronic energy levels, and g factors are computed. Electron correlation is shown to have a substantial effect on the Jahn-Teller properties. As have others, we find the Jahn-Teller effect in VCl4 to be of the dynamic form.

Publisher's Note: “Tunneling splittings in vibronic energy levels of CH3F+ (${\rm \tilde X}^2 {\rm E}$X̃2E) studied by high resolution photoelectron spectroscopy and ab initio calculation” [J. Chem. Phys. 139, 064302 (2013)

Publisher's Note: “Tunneling splittings in vibronic energy levels of CH3F+ (${\rm \tilde X}^2 {\rm E}$X̃2E) studied by high resolution photoelectron spectroscopy and <i>ab initio</i> calculation” [J. Chem. Phys. 139, 064302 (2013)

Tunneling splittings in vibronic energy levels of CH 3F+X̃2E studied by high resolution photoelectron spectroscopy and ab initio calculation

The energy levels of CH3F(+) (X(2)E), which show strong vibronic coupling effect (Jahn-Teller effect), have been measured up to 3500 cm(-1) above the ground vibrational state using one-photon zero-kinetic energy photoelectron spectroscopic method. Theoretical calculations have also been performed to calculate the spin-vibronic energy levels using a diabatic model and ab initio adiabatic potential energy surfaces (APESs) including the energy gradients and derivative couplings between the APESs. The calculations showed that the tunneling splittings of the vibrational energy levels occur due to the deep potential energy wells formed by the Jahn-Teller deformation. The calculated spin-vibronic energy levels are in good agreement with the experimental data. For example, the energy splitting for the first excited vibrational energy level is calculated as 111 cm(-1) that is confirmed by the experimental value. The experimental spectrum was assigned based on the fundamental vibrational modes calculated at the energy minimum. The fundamental vibrational modes related to the H-C-F bending, H-C-H bending, C-F stretching, and C-H stretching vibrations have been observed.