2Π State Research Articles

Spectroscopic Study of the B 1Π State of NaH.

In this study, the B1Π excited state of NaH has been experimentally studied for the first time. Pulsed laser-induced fluorescence excitation spectroscopy was used to investigate the B1Π electronic state of NaH. A total of 48 ro-vibronic transitions were observed, including within the B–X (0–0) and B–X (0–1) transition bands. Only one B-state vibrational level was identified, and a series of PQR lines, with eight e-parity and eight f-parity sublevels (v′ = 0, J′ = 1–8), were assigned. The level assignment was supported by a comparison of the experimental line positions with the ab initio calculations, the dispersed laser-induced fluorescence spectrum of the NaH B1Π → X1∑+ emission, and the V-type optical–optical double resonance spectra. The Dunham-type coefficients, the mean internuclear distance, the harmonic vibrational frequency ω, and the dissociation energies D0 and De of the B1Π state were determined.

Confinement of stable skyrmionium and skyrmion state in ultrathin nanoring

Magnetic skyrmionium is a donut-shaped spin texture with zero topological number (Q) and has promising application in future spintronic devices. In this work, using micromagnetic simulation based on Landau-Lifshitz-Gilbert (LLG) equation, we report the generation of skyrmionium in an ultrathin magnetic nanoring in the presence of Dzyaloshinskii-Moriya interaction (DMI) and external magnetic field. By varying the DMI strength and outer diameter of a nanoring, the possibilities of creation of other skyrmion states (kπ states) are explored and we have reported the existence of 3π state and 4π state in nanoring for the first time. Also, we report that the transition of skyrmion state from kπ to (k-1)π occurs for a few millitesla (mT) magnetic fields in the out-of-plane configuration. Further, we have demonstrated the degeneration of skyrmionium (Q=0) into an isolated skyrmion (Q=±1) and a pair of skyrmions (Q=−2) in a nanoring of small dimension by applying an in-plane spin-polarized current. A complete study of the generation of skyrmionium and its topological stability is done by performing the micromagnetic simulation. Our results will provide guidelines for the design of spin-polarized current-controlled skyrmionium-skyrmion based spintronic memory and logic devices.

The Connection between Pseudo-Jahn–Teller Effect and Electron Delocalization for Proving the Origin of Equilibrium Geometry of Nitrosyl Halides (Halides = Cl, Br, and I)

The theoretical calculations on triplet linear and non-linear structures of nitrosyl halides XNO (X = Cl, Br, and I) confirm that the origin of instability and symmetry breaking of XNO linear structures is a pseudo-Jahn–Teller effect (PJTE). However, the PJTE associated with electron delocalization may prove the stability of XNO non-linear structures best. The distortion of high-symmetry (C∞v) configurations in XNOs emerges from mixing the PJT with ground 3Σ– and the excited 3Π states in the Qπ direction, which consequently make the ground state unstable. The PJT problem is formulated in the form (3Σ– + 3Π) $$ \otimes $$ π. The energy difference between high-symmetry C∞v geometries and low-symmetry Cs geometries energy gap between the ground and excited states decreases from ClNO to INO. Also, ΔEPJT (i.e., the difference of energy between the highest occupied molecular orbital (HOMO; LPX), and the lowest unoccupied molecular orbital (LUMO; $$\pi _{{{\text{NO}}}}^{*}$$ )) plays an important role in the instability of structures. Electron delocalization decreases and PJT instability increases from ClNO to INO in high-symmetry C∞v geometries. According to the results of the canonical molecular orbital (CMO) analysis, the contribution of the LPX non-bonding orbitals in the vibronic coupling constant (F) increases from ClNO to INO. Also, the NBODEL results indicate that the instability of compounds increases from ClNO to INO. Because the primary force constant is positive, the curvature of ground electronic state configuration curves in adiabatic potential energy surfaces (APESs) decreases from ClNO to INO. The variations of the chemical hardness differences between the non-linear (Cs) and linear (C∞v) structures decrease from ClNO to INO and of chemical potential differences increase from ClNO to INO, justifying the variation trend of ΔEPJT. Furthermore, based on the obtained results, Δ[η(Cs) – η(C∞v)] obeys the maximum hardness principle.

Stability phase diagrams and tuning of magnetic skyrmionium and other states

Topological magnetic states such as skyrmions have widely been investigated as a suitable candidate for memory bits in next generation data storage device applications including random access memory (RAM) or race-track memory as well as spin-torque nano-oscillators etc. Energy efficient multistate switching of these states based on electric control of magnetization involves the electric field tuning of perpendicular magnetic anisotropy (PMA). By using micromagnetic simulation study, we demonstrate the strain-mediated electric manipulation of various topological magnetic states in nanodisc with [Pt/Co/Ta]n trilayer stacks residing on a piezoelectric substrate. A stability phase diagram is derived for the representation of regions of the lowest energy states against the applied strain as a function of disc dimensions. Utilizing this derived phase diagram, various electric field-induced strain-mediated switching scenarios including non-volatile reversible switching of skyrmion into skyrmionium, 3π state and helical stripe domain state, the creation of skyrmionium from uniform single-domain magnetic state and its annihilation and volatile reversible switching between skyrmionium and vortex are achieved. Moreover, an extended phase diagram based on the estimated critical values of the applied strain for different domain structures within the nanodisc is also built and further implemented in designing a multistate sequential switching between various magnetic states triggered by a continuously varying strain pulse. These findings hold a potential for contributing in the development of low-power high-density multistate magneto-electric or magneto-elastic memory and logic device applications involving simple architectural concept applicable to future microelectronic integrated device strategies.

Direct Observation of the C + S2 Channel in CS2 Photodissociation.

Carbon disulfide (CS2) is a typical triatomic molecule. Its photodissociation process has generally been assumed to proceed to CS and S primary products via single bond fission. However, recent theoretical calculations suggested that an exit channel to produce C + S2 should also be energetically accessible. Here, we report the direct experimental evidence for the C + S2 channel in CS2 photodissociation by using the velocity map ion imaging technique with two-photon UV and one-photon vacuum UV (VUV) excitations. The detection of the C (3P) products illustrates that the ground state and the electronically excited states of S2 coproducts are formed within highly excited vibrational states. The very weak anisotropic distributions indicate relatively slow dissociation processes. The possible dissociation mechanism involves molecular isomerization of CS2 to linear-CSS from the excited 1B2 (21Σ+) state via vibronic coupling with the 1Π state followed by an avoided crossing with the ground state surface. Our results imply that the S2 molecules observed in comets might be primarily formed in CS2 photodissociation.

Laboratory Study of the Cameron Bands, the First Negative Bands, and Fourth Positive Bands in the Middle Ultraviolet 180–280 nm by Electron Impact Upon CO

AbstractWe have analyzed medium‐resolution (full width at half maximum, FWHM = 1.2 nm), Middle UltraViolet (MUV; 180–280 nm) laboratory emission spectra of carbon monoxide (CO) excited by electron impact at 15, 20, 40, 50, and 100 eV under single‐scattering conditions at 300 K. The MUV emission spectra at 100 eV contain the Cameron Bands (CB) CO(a 3Π → X 1Σ+), the fourth positive group (4PG) CO(A 1Π → X 1Σ+), and the first negative group (1NG) CO+(B 2Σ+ → X 2Σ) from direct excitation and cascading‐induced emission of an optically thin CO gas. We have determined vibrational intensities and emission cross sections for these systems, important for modeling UV observations of the atmospheres of Mars and Venus. We have also measured the CB “glow” profile about the electron beam of the long‐lived CO (a 3Π) state and determined its average metastable lifetime of 3 ± 1 ms. Optically allowed cascading from a host of triplet states has been found to be the dominant excitation process contributing to the CB emission cross section at 15 eV, most strongly by the d 3Δ and a' 3Σ+ electronic states. We normalized the CB emission cross section at 15 eV electron impact energy by multilinear regression (MLR) analysis to the blended 15 eV MUV spectrum over the spectral range of 180–280 nm, based on the 4PG emission cross section at 15 eV that we have previously measured (Ajello et al., 2019, https://doi.org/10.1029/2018ja026308). We find the CB total emission cross section at 15 eV to be 7.7 × 10−17 cm2.

Природа тонкой структуры вращательных уровней основного X-=SUP=-2-=/SUP=-Sigma-=SUP=-+-=/SUP=--состояния радикала CN

By means of ab initio high-level quantum-chemical calculations of non-diagonal matrix elements of spin-orbital and electron-rotational coupling between the ground X2Σ+ and excited (1--4)2Π states the observed regular effect of γ-doubling of the rotational levels of the X2Σ+ state was shown to be mainly determined by intramolecular interactions of the mentioned state with remote states (2--4)2Π. In terms of the nonadiabatic model of the effective radial Hamiltonian of the isolated electronic state, it was possible to create the analytical potential of the X2Σ+ state and the corresponding function γ (R) reproducing the frequencies of rotational and vibrational-rotational transitions (for the lowest vibrational levels ν≤3) of the CN molecule at the experimental (spectroscopic) level of accuracy.

Exploring the excited states of the GeH+ radical cation including spin-orbit interaction: A revisited study

In this paper, we have carried out high-level ab initio calculations on the electronic states of GeH+ with the configuration interaction method. The spin-orbit coupling (SOC), core-valence correlation (CV), scalar relativistic effects and Davidson correction (+Q) are included. The potential energy curves (PECs) of 13 Λ-S correlated with the four lowest dissociation limits and 32 Ω electronic states generated from those Λ-S states are obtained. Our results indicate that the first 3Σ− and second 3Π states are adiabatically correlated with the dissociation limit Ge(3Pg) + H+(1S), which is different from the previously reported Ge+(4Pg) + H(2Sg). From the computed PECs, the spectroscopic constants of the Λ-S and Ω states are determined, which are in good agreement with previous experiments. The dipole moments (DMs) for Λ-S electronic states are also investigated. With the help of spin-orbit coupling matrix involving the 13Σ− and 23Π states, the intricate couplings related with the crossing states are revealed, and the weak predissociation for ν' ≥0 vibrational levels of 13Σ− and the perturbations for vibrational levels of 21Σ+ (ν' ≥1) and 11Δ (ν' ≥0) states are analyzed. Finally, the transition properties of five transitions are predicted, including the Franck-Condon Factors (FCFs), transition dipole moments (TDMs), and the spontaneous radiative lifetimes of lower vibrational states. This study will improve our comprehension on the detailed electronic structure and spectroscopy of GeH+ radical cation.

Characterisation of the b 3Σ+, v = 0 state and its interaction with the A 1Π state in aluminium monofluoride

Recently, we determined the detailed energy level structure of the , and states of AlF that are relevant to laser cooling and trapping experiments [Truppe et al., Phys. Rev. A. 100 (5), 052513 (2019)]. Here, we investigate the state of the AlF molecule. A rotationally resolved (1 + 2)-REMPI spectrum of the band is presented and the lifetime of the state is measured to be 190(2) ns. Hyperfine-resolved, laser-induced fluorescence spectra of the and the bands are recorded to determine fine- and hyperfine structure parameters. The interaction between the and the nearby state is studied and the magnitude of the spin–orbit coupling between the two electronic states is derived using three independent methods to give a consistent value of 10(1) cm. The triplet character of the A state causes an loss from the main A−X laser cooling cycle below the 10 level.

Electronic structure and bonding of the ScNH and YNH molecules

We report the results of multi-reference configuration interaction calculations of the electronic and geometric structures of the X2Σ+, B2Σ+, Ã2Πi, Ã2Πr &2Δ states of the transition metal imides, ScNH and YNH, and compare with the available experimental data. The metal is bonded to the NH group by a double bond in the π system for all states. There are 4 π electrons in the X2Σ+, B2Σ+, Ã2Πr &2Δ states and 3 in the Ã2Πi. The atomic orbital composition in the 4π states is remarkably similar, the average being 75%2pπ+21%dπ+4%pπ while in the 3π state we have 88%2pπ+10%dπ+2%pπ.

High-Resolution Photoelectron Imaging and Photodetachment Spectroscopy of Cryogenically Cooled IO–

We report a high-resolution photoelectron imaging and photodetachment spectroscopy study of cryogenically-cooled IO-. The high-resolution photoelectron spectra yield a more accurate electron affinity (EA) of 2.3805(5) eV for IO, as well as a more accurate spin-orbit splitting energy between 2Π3/2 and 2Π1/2 of IO as 2093(5) cm-1. Photodetachment spectroscopy revealed for the first time several excited states for the IO- anion, including two valence-type excited states, the repulsive 3Π state and a shallow bound 1Π state. More interestingly, we have observed two vibrational resonances which are proposed to be due to a dipole-induced resonant state, about 230 cm-1 above the detachment threshold of IO-.

A study of the valence shell absolute photoabsorption, photoionization and photodissociation cross sections, and the photoionization quantum efficiency of carbon monoxide

The spectroscopic characteristics and the decay mechanisms of the Rydberg states arising from valence shell excitations in carbon monoxide have been investigated by using a double ion chamber and synchrotron radiation to measure the absolute photoabsorption, photoionization and photodissociation cross sections, and the photoionization quantum efficiency, in the energy range between the ionization threshold and 36 eV. Guided by earlier theoretical predictions, the prominent absorption bands due to Rydberg states belonging to series converging onto the A 2Π state ionization threshold have been assigned, in accord with previous studies, to the ndδ and the [(n + 1)s + nd]σ transitions. Apart from the (4s + 3d)σ state which decays predominantly by predissociation into neutral fragments, most of the Rydberg states belonging to these series decay preferentially by autoionization. Another Rydberg series converging onto the A 2Π state limit has been tentatively assigned to the npσ transitions, even though these transitions are predicted to be weak. The v′ = 0 and v′ = 1 vibrational levels of the 4pσ state decay preferentially by predissociation into neutral fragments. The [(n + 1)s − nd]σ transitions are also calculated to be weak but may be associated with some previously unassigned absorption bands. Structure observed in the absorption spectrum between ∼19.5 and 23.5 eV may be due to Rydberg states associated with series converging onto the D 2Π or the 3 2Σ+ state limits. This structure is discussed in relation to dispersed fluorescence spectra and negative ion yields recorded over the same energy range.

Vibrationally resolved electron impact electronic excitation of BeH

Beryllium is being adopted for plasma facing walls in fusion reactors. This has led to the observation of emissions from the A 2Π state of beryllium hydride. Use of these emissions to monitor Be erosion requires electron impact excitation rates. Cross sections for electron impact vibrational excitation within the X 2Σ+ state and vibrationally resolved electronic excitation to the A 2Π state are reported for BeH, BeD and BeT. Electron collisions are studied at a range of internuclear separations using the UK molecular R-matrix (UKRmol+) codes. Electronic excitation is studied both within the Franck–Condon approximation and by explicit averaging of the T-matrix elements. It is found that (a) inclusion of the effect of higher partial waves using the Born approximation leads to significant increases in the cross sections and (b) the Franck–Condon approximation underestimates the importance of collisions for which the vibrational state changes during electronic excitation.

Ab initio complex potential energy curves of the He*(1s2p1P)-Li dimer.

LiHe is an intriguing open-shell dimer. It is an extremely weakly bound system, and its vibrational bound-state radius extends far into the classically forbidden regions. Exciting helium into 1s2p leads to a 2Σ and a 2Π state, in which lithium is in its ground state. These states are located above the ionization threshold of the Li atom, which makes them metastable, i.e., resonance states. Under these conditions, energy transfer between the atoms over large distances is feasible within the framework of interatomic Coulombic decay (ICD). These states are investigated theoretically; herein, we present and analyze the complex potential energy curves of the 2Σ and 2Π states, where their imaginary parts describe the decay rate of these resonance states. We employ the resonance via Padé approach to calculate these potentials. Thereby, we use the equation-of-motion coupled-cluster method to compute stabilization graphs as input data for the analytical dilation (via Padé) into the complex energy plane. The procedure is suitable for studying Feshbach resonances and ICD states such as the LiHe 2Σ and 2Π states. The resulting ab initio complex potential energy curves will be used in future work to describe the dynamics of the process HeLi + hν → He*Li → HeLi+ + eICD, which is amenable to experiment.

Rovibrational transition properties of the X1Σ+ and A1Π states of carbon monosulfide

Carbon monosulfide was detected in outer space by rovibrational spectroscopy of the X 1Σ+ state and A 1Π – X 1Σ+ system. This work calculated the potential energy curves and dipole moment functions of the X 1Σ+ 0+ and A 1Π1 states, and computed the transition dipole moments between the two states employing the CASSCF method, followed by the valence icMRCI approach. Core-valence correlation and scalar relativistic corrections were included. The extrapolation of potential energies to the complete basis set limit was performed. The spin-orbit coupling effect was included. The Einstein A coefficients, band origins, and oscillator strengths were calculated for the rovibrational transitions when J ≤ 150. The rovibrational transitions of the X 1Σ+ 0+ and A 1Π1 states became very weak when Δυ ≥ 6. The Einstein A coefficients of vibronic emissions of the A 1Π1 – X 1Σ+ 0+ system were large, indicating that the emissions were able to be measured easily through spectroscopy. Several rovibrational transitions of the A 1Π1 – X 1Σ+ 0+ system were analysed in detail. The distribution of radiative lifetime varying as rotational quantum number was calculated. The results obtained in this work agree well with the available experimental values.

Perturbations of the A′1Π and C1Σ+ states of CaO

Laser induced fluorescence spectra for jet-cooled CaO have been used to examine the higher vibrational levels of the A′1Π(Xσπ−1) state (v = 10–17) and the v = 6–8 vibrational levels of the C1Σ+(Bσσ−1) state. A perturbation of v = 17 of the A′ state was evident, caused by a spin-orbit mediated interaction with the b3Σ+(Ω = 1)(Xσσ−1) v = 14 level. Ro-vibrational constants for the A′ state were obtained by fitting to the data for nominally unperturbed levels. The average radiative lifetime for the A′1Π(Xσπ−1) state v = 10–17 levels was 2.6 μs, with no measurable dependence on v. This was consistent with the theoretical prediction of a relatively small transition dipole moment for the A′1Π–X1Σ+ band system.A homogeneous perturbation of the C1Σ+(Bσσ−1) v = 7 level was examined by means of dispersed laser induced fluorescence (DLIF) and radiative lifetime measurements. The DLIF spectra clearly demonstrate that the perturbing Ω = 0+ state is a component of a triplet state. Intense transitions from this state to the a3Π(0+)(Xσπ−1) state were observed. Configurational arguments are presented that support assignment of the perturbing state as the v = 12 vibrational level of the previously unobserved g3Π(0+)(Bσπ−1) state.

Exploring excited electronic states: A theoretical contribution to the spectroscopy of strontium monochloride, SrCl

The Λ + S and Ω electronic states of strontium monochloride are characterized at the CASSCF/MRCI+Q level of theory. For the first time, reliable potential energy curves and associated spectroscopic parameters, as well as dipole moment and transition dipole moment functions are reported. Transition probabilities given by the Einstein coefficients for spontaneous emission, and the associated radiative lifetimes provide relevant information on the relative intensities of the various bands systems. Accurate dissociation energies were determined for the ground and excited states, and a set of spin-orbit constants derived for the 2Π and 2Δ states. Electronic transitions involving a new bound state A´ 2Δ offer new routes to spectroscopic studies. Radiative lifetimes for the states A 2Π, B 2Σ+, and C 2Δ show good agreement with experimental ones. The suggestion in the literature of an avoided crossing involving the B 2Σ+ state to explain a local perturbation in the spectra is not corroborated in this study. The present results should provide a clear perspective to guide future experimental investigations of electronic transitions on this system.

The coupled system (2)2Σ+ and (1)2Π of 7Li88Sr

We analyse rovibrational transitions of the (2)2Σ+–X(1)2Σ+ system of LiSr and find the energy levels of the (2)2Σ+ state to be perturbed by coupling between the (2)2Σ+ and (1)2Π states. We present an analysis of the coupled system yielding molecular parameters for the lowest vibrational levels of the (2)2Σ+ state and for higher vibrational levels of the (1)2Π state together with molecular coupling constants. Improved Dunham coefficients for the rovibrational levels of the X(1)2Σ+ state are also obtained, where the correlation with the parameters of the excited states is removed completely.

Reinvestigate the C2Π-X2Π(0,0) band of AgO

The C2Π-X2Π(0,0) band of AgO has been reinvestigated by laser induced fluorescence spectroscopy with a spectral resolution of ∼0.02 cm−1. The AgO molecules are produced by discharging a gas mixture of O2/Ar with silver needle electrodes in a supersonic jet expansion. By employing a home-made narrowband single longitude mode optical parametric oscillator (SLM-OPO) as the laser source, high-resolution spectra of the C2Π-X2Π(0,0) band have been recorded for both 107Ag16O and 109Ag16O isotopologues. The spectroscopic constants of the C2Π state are consequently determined, with the 109Ag16O one being reported for the first time. The nature of the spin-orbit coupling effect in the C2Π state is proposed to be due to state mixing with the nearby repulsive 4Σ− and 4Π states.

Rotational and hyperfine analysis of the A2∑+ - X1 2π3/2 and B2∑- - X1 2π3/2 transitions of AuS

We have recorded the (0,0) and (0,0) bands of gold monosulphide (AuS) at sub-Doppler resolution by intermodulated fluorescence spectroscopy. These two red-degraded bands lie at 642.3 and 613.8 nm, respectively. The high resolution of the experiment enabled the accurate determination of the rotational, fine and 197Au hyperfine constants of the two excited states for the first time. The Fermi contact dipolar and electric quadrupolar interactions in the upper states can be understood in terms of the electronic configurations from which they arise. The signs of the spin–rotation parameters, γ(A2Σ+) = −0.080821(24) cm−1 and γ(B2Σ−) = 0.136427(20) cm−1, suggest that the fine structures of these states arise primarily by interactions with inverted 2Π states lying at higher energy.