Excited State Potential Curves Research Articles

Chemically Accurate Potential Curves for H2 Molecules Using Explicitly Correlated Qubit-ADAPT.

With the recent advances in the development of devices capable of performing quantum computations, a growing interest in finding near-term applications has emerged in many areas of science. In the era of nonfault tolerant quantum devices, algorithms that only require comparably short circuits accompanied by high repetition rates are considered to be a promising approach for assisting classical machines with finding a solution on computationally hard problems. The ADAPT approach previously introduced in Nat. Commun. 10, 3007 (2019) extends the class of variational quantum eigensolver algorithms with dynamically growing ansätze in order to find approximations to the ground and excited state energies of molecules. In this work, the ADAPT algorithm has been combined with a first-quantized formulation for the hydrogen molecule in the Born-Oppenheimer approximation, employing the explicitly correlated basis functions introduced in J. Chem. Phys. 43, 2429 (1965). By the virtue of their explicit electronic correlation properties, it is shown in classically performed simulations that chemical accuracy (<1.6 mHa) can be reached for ground and excited state potential curves using reasonably short circuits.

Quasi-Molecular Optical Transitions near Resonance Lines of Kr and Xe Atoms in Helium

The emission and absorption spectra of Kr and Xe atoms near the 1,3P1–1S0 resonance lines in an atmosphere of helium atoms under equilibrium conditions have been theoretically investigated. Potential curves for excited states of Kr(4p55s) + He and Xe(5p56s) + He quasi-molecules are obtained with joint application of the effective Hamiltonian and pseudopotential methods. Experimental data are used for the ground state. Based on these potential curves, the spectral profiles of quasi-molecular emission and absorption for short-wavelength wings of the resonance lines are calculated within the quasi-static approximation. The results obtained for absorption are compared with the known experimental data.

Calculation of the Radiative Parameters for the (2)2Σ+–X2Σ+ Electronic Transition of NaK+ and NaCs+ Molecular Ions

Einstein spontaneous radiation coefficients, absorption oscillator strengths, Franck–Condon factors, wavenumbers of vibronic transitions in (2)2Σ+–X2Σ+ band systems of NaK+ (0 ≤ v′ ≤ 14, 0 ≤ v′′ ≤ 100) and NaCs+ molecular ions (0 ≤ v′ < 14, 0 ≤ v′′ ≤ 69), and excited electronic-state radiative lifetimes are calculated using Hulburt–Hirschfelder potential curves for ground and excited electronic states that were constructed using published ab initio calculations. Vibrational energies and the corresponding wave functions necessary to calculate radiative parameters were found by numerical solution of the Schrodinger equation.

Quantum optimal control pathways of ozone isomerization dynamics subject to competing dissociation: A two-state one-dimensional model

We construct a two-state one-dimensional reaction-path model for ozone open → cyclic isomerization dynamics. The model is based on the intrinsic reaction coordinate connecting the cyclic and open isomers with the O2 + O asymptote on the ground-state (1)A(') potential energy surface obtained with the high-level ab initio method. Using this two-state model time-dependent wave packet optimal control simulations are carried out. Two possible pathways are identified along with their respective band-limited optimal control fields; for pathway 1 the wave packet initially associated with the open isomer is first pumped into a shallow well on the excited electronic state potential curve and then driven back to the ground electronic state to form the cyclic isomer, whereas for pathway 2 the corresponding wave packet is excited directly to the primary well of the excited state potential curve. The simulations reveal that the optimal field for pathway 1 produces a final yield of nearly 100% with substantially smaller intensity than that obtained in a previous study [Y. Kurosaki, M. Artamonov, T.-S. Ho, and H. Rabitz, J. Chem. Phys. 131, 044306 (2009)] using a single-state one-dimensional model. Pathway 2, due to its strong coupling to the dissociation channel, is less effective than pathway 1. The simulations also show that nonlinear field effects due to molecular polarizability and hyperpolarizability are small for pathway 1 but could become significant for pathway 2 because much higher field intensity is involved in the latter. The results suggest that a practical control may be feasible with the aid of a few lowly excited electronic states for ozone isomerization.

Electronic spectra of XeNe molecules in the range 77100-90100 cm-1 near Xe* (6p, 5d, 6p’, 7s, 7p, 6d) obtained by the (3 + 1) REMPI and (2 + 1) REMPI methods

The electronic spectra of XeNe molecules in the range of 77100-90100 cm-1 are measured by the method of laser resonance multiphoton ionization in a supersonic jet. The photoionization spectra are obtained upon two- and three-photon excitations of molecules and their ionization by the next photon. In the range of 80300-90100 cm-1 near Xe*(5d, 6p’, 6d, 7s, and 7p), the spectra are obtained for the first time. A whole number of vibrational systems are measured in this range. The majority of vibrational systems near Xe* (5d, 6d, 7p, and 7s) are located in the red range with respect to their dissociation limits. In the blue range with respect to the dissociation limits, continua corresponding to transitions of molecules from the ground state to repulsive potential curves of excited states are detected. For a number of excited states of XeNe molecules, the vibrational analysis is performed and molecular constants are estimated.

Photoemission into water adsorbed on metals: Probing dissociative electron transfer using theory

AbstractThe photoinduced dissociation of water adsorbed on a silver nanoparticle is explored using theory to probe reaction pathways that produce hydrogen. Ab initio configuration theory is used to describe the systems. A formulation that allows excited electronic states embedded in a near continuum of lower energy states to be calculated accurately is described. Electron attachment of a photoemitted electron to adsorbed water can lead to the formation of H2 at a very low energy barrier with oxygen remaining on the Ag surface. A large energy barrier to form H2 plus adsorbed O is found for the ground state. The excited state has a much smaller barrier to OH stretch; however, to dissociate, the system must cross over from the excited state to the ground state potential energy surface. The cross over point is near the transition state for a ground state process. A characteristic feature of the excited state potential curve is an increase in energy in the early stages of OH stretch as the charge transfer state evolves from a state with considerable Rydberg character to one that has a typical OH antibonding molecular orbital. Another pathway releases a H atom leaving OH on the surface. Effects due to doping of a Ag nanoparticle with a K electron donor atom are compared with those caused by a Fermi level shift due to an applied potential. Results are also reported for electron transfer to a solvated lithium ion, Li(H2O), near the surface of a silver particle. A steering mechanism is found that involves the interaction of a hydridic hydrogen formed after electron transfer with an acidic hydrogen of a second solvated water molecule. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Ab initio potential energy curves, transition dipole moments and spin–orbit coupling matrix elements for the first twenty states of the calcium dimer§

State-of-the-art ab initio techniques have been applied to compute the potential energy curves of the calcium diatom in the Born–Oppenheimer approximation for the first twenty singlet and triplet states dissociating into 3P+1S, 3D+1S, 1D+1S and 1P+1S atomic states. All the excited state potential curves were computed using a combination of the linear response theory within the coupled-cluster singles and doubles framework for the core–core and core–valence electronic correlation with the full configuration interaction for the valence–valence correlation. The electric and magnetic transition dipole moments governing the X and X, respectively, have been obtained as the first residue of the polarization propagator computed with the linear response coupled-cluster method restricted to single and double excitations. Spin–orbit coupling matrix elements have been evaluated within the complete active space self-consistent field framework using an effective core potential from the Cowan–Griffin relativistic ab initio model potential method. With these couplings, the spin–orbit coupled potential energy curves for the and 1 u states of the calcium diatom have been obtained. Our results are compared with other ab initio calculations and with the experimental data available for the calcium diatom. §Dedicated to Professor Andrzej J. Sadlej on the occasion of his 65th birthday.

Absorption spectra of Zn–Kr around the Zn (41P1–41S0) resonance line: experimental and theoretical studies

The absorption spectrum accompanying the Zn (41P1–41S0) 213.8 nm resonance line in the presence of 1.613 × 1019 atoms/cm3 of Kr is carefully measured and the absolute absorption coefficient per atom pair is derived. The rainbow satellites associated with ZnKr (10+ ← X) free–free transitions on both line wings are observed and utilized for probing the excited state potential curve by means of quantum simulation of the spectrum. Best available theoretical potential curves were employed as the input data. It is found that the simulated red wing profile including the satellite agrees with the experimental one quite well. However, in the case of the blue satellite a considerable correction of the 10+ state potential at short interatomic distances proved to be necessary in order to reproduce the spectral position and the shape of the experimental band. Van der Waals constants describing the long-range behaviour of the excited states 10+ and 11 potential curves are derived from the near red wing profile analysis.

The excited electronic states and the ionization potential of the AlND3 complex

The AlND3 complex was studied in a molecular beam by resonant one-color two-photon and two-color two-photon photoionization techniques with a resolution of 0.3 cm−1. Six progressions of bands were observed in the 18 100–26 200 cm−1 (381–552 nm) region. One progression (ωe=316±0.8 cm−1) was assigned to the Al–ND3 stretch (ν3′) in the B̃2A1 state correlating with the 3s 2S term of Al. The origin of the B̃2A1–X̃2E1/2 system was found at 18 532.5±0.7 cm−1. The second (ωe=428±2 cm−1) and third (ωe=594±12 cm−1) progressions were assigned to the Al–ND3 stretch (ν3′) and the bend (ν6′) in the C̃2E state correlating with the 3d 2D term of Al. The origin of the C̃2E–X̃2E1/2 system was found at 21 185±5 cm−1. Assignments of the other three progressions with origins and harmonic wave numbers of 22 667±2 and 358±2 cm−1; 24 382±10 and 432±10 cm−1; and ∼21 871 and ∼1050 cm−1 remain uncertain. The spin-orbit splitting of the X̃2E ground state was determined to be 55.8±0.7 cm−1. Several Rydberg series converging to the v3+=1, 2, and 3 levels of the ground state of the AlND3+ ion were observed. The ionization potential of the AlND3 complex was measured to be 39 710±2 cm−1. The ν3+ fundamental in the ground state of the AlND3+ ion was found to be 325±5 cm−1. To aid the interpretation of our spectra, ab initio optimized structures and vibrational wave numbers for the ground states of various isotopomers of AlNH3 and AlNH3+ were calculated. Also, Al–NH3 potential curves for several low-lying excited states were calculated. In addition, the ionization potential of the AlNH3 isotopomer was measured by the one-photon photoionization efficiency technique. The value of 39 760±10 cm−1 is an improvement on that previously reported by Di Palma et al. [Chem. Phys. Lett. 284, 184 (1998)], which was 180 cm−1 smaller.

Comment on `Potential energy surfaces of excited states of H 2−' (Chem. Phys. Lett. 285 (1998) 114–120)

The H 2 − excited state potential curves of Mebel et al. (Chem. Phys. Lett. 285 (1998) 114–120) are re-analysed. They are shown to be artefacts of the method of computation, with little or no relation to real states. The need for caution in the use of bound state electronic structure methods to study resonance parameters is re-emphasized.

Potential energy curves of ICl and non-adiabatic interactions studied by the spin-orbit CI method

Excited state potential curves of ICl have been obtained by the spin–orbit CI method to describe the non-adiabatic interactions. Variations of each wavefunction are analyzed and three avoided crossings are characterized between 0 +(III)/0 +(IV), 0 +(II)/0 +(IV), and 0 +(II)/0 +(III) at R=2.85, 3.14 and 3.62 Å, respectively. The second avoided crossing, that was suggested before by Tiemann et al. is proved here for the first time. Our 1Π 1, 1(II) state crosses with the B state just inside the second avoided crossing, supporting the experimental analyses made by Gordon et al. and Tiemann et al. Applying to the B state photodissociation, our potential curves yield the wavelength dependence of the branching ratios, I( 2P 3/2)+Cl( 2P 3/2)/I( 2P 3/2)+Cl( 2P 1/2), in good agreement with experimental results. Photodissociation from the second absorption band is also discussed based on our theoretical and recent experimental results.

Excited electronic states of carbon disulphide

The near-ultraviolet spectrum of CS2 is studied thoroughly using high level CISTDQ and EOM-CCSD theory with DZP and TZ2P(f) basis sets. Potential energy curves of the first seven singly excited states with respect to the SCS bond angle have been predicted. The relative energy ordering of the excited states as established at the equilibrium geometries using EOM-CCSD theory is: X˜1Σ+g, < a3B2 < b˜3A2(R) < A1A2 < c˜3B2 < B˜1B2 (V) < d˜3A2 < C˜1A2, which is at odds with previous theoretical work. The bent B˜1B2 state arises from the Renner—Teller splitting of a linear 1Δu state into 1B2 and 1A2 states. In disagreement with previous experimental predictions that the 1A2 state is the lower lying component of this splitting, it is firmly established from the high level results in this research that the C˜1A2 state is the higher lying component of this Renner—Teller pair. Equilibrium geometries are determined and shown to agree qualitatively with experiment, save for the B˜1B2 state. From an analysis of the complex rotational structure of the V band the experimental geometry of the B˜1B2 state was determined to be slightly bent (re = 1.544 Å, θe = 160°), whereas the methods employed in this research predict a significantly bent geometry (re = 1.632 Å, θe = 132.1° at EOM-CCSD/TZ2P(f)). Relative transition energies, Te, are predicted, and EOM-CCSD calculations are shown to agree well with available experimental data, and show the assignment of the V and R bands to be correct while the T band is correctly assigned to the A1A2 state and not the lower lying Renner—Teller component of the 1Δu state. The high level CI methods, although yielding qualitatively correct potential energy curves, do not provide quantitatively accurate transition energies, and it is clear that even an exhaustive treatment of the eight valence π electrons is not entirely satisfactory, while EOM-CCSD is established as an accurate method for the prediction of excited state potential curves.

Excited electronic states of carbon disulphide

The near-ultraviolet spectrum of CS2 is studied thoroughly using high level CISTDQ and EOM-CCSD theory with DZP and TZ2P(f) basis sets. Potential energy curves of the first seven singly excited states with respect to the SCS bond angle have been predicted. The relative energy ordering of the excited states as established at the equilibrium geometries using EOM-CCSD theory is: X˜1Σ+g, < a3B2 < b˜3A2(R) < A1A2 < c˜3B2 < B˜1B2 (V) < d˜3A2 < C˜1A2, which is at odds with previous theoretical work. The bent B˜1B2 state arises from the Renner—Teller splitting of a linear 1Δu state into 1B2 and 1A2 states. In disagreement with previous experimental predictions that the 1A2 state is the lower lying component of this splitting, it is firmly established from the high level results in this research that the C˜1A2 state is the higher lying component of this Renner—Teller pair. Equilibrium geometries are determined and shown to agree qualitatively with experiment, save for the B˜1B2 state. From an analysis of the complex rotational structure of the V band the experimental geometry of the B˜1B2 state was determined to be slightly bent (re = 1.544 Å, θe = 160°), whereas the methods employed in this research predict a significantly bent geometry (re = 1.632 Å, θe = 132.1° at EOM-CCSD/TZ2P(f)). Relative transition energies, Te, are predicted, and EOM-CCSD calculations are shown to agree well with available experimental data, and show the assignment of the V and R bands to be correct while the T band is correctly assigned to the A1A2 state and not the lower lying Renner—Teller component of the 1Δu state. The high level CI methods, although yielding qualitatively correct potential energy curves, do not provide quantitatively accurate transition energies, and it is clear that even an exhaustive treatment of the eight valence π electrons is not entirely satisfactory, while EOM-CCSD is established as an accurate method for the prediction of excited state potential curves.

The ultraviolet absorption spectrum of hot carbon dioxide

The vacuum ultraviolet absorption spectrum of CO 2 shifts significantly to longer wavelengths with increasing temperature. We have measured this temperature dependence and present absorption cross sections for 230 to 355 nm at temperatures from 1523 to 2273 K. At 2273 K this red shift extends the absorption above 300 nm and well into the blue end of the solar spectrum. In CO 2 the thermal shift is enhanced because of the relative position and shapes of the excited and ground state potential curves.

Model potential calculations for the excited and Rydberg states of the Na2+ molecular ion: Potential curves, dipole and quadrupole transition moments

Molecular potential curves for many excited states of the Na2 molecule are presently available for a wide range of internuclear distances, in the framework of a two-electron model potential method. The energies were obtained through an extensive configuration interaction procedure using Na+ 2 orbitals, and the quality of the results was controlled by the accuracy of the wavefunctions of the molecular ion. In this work, computed potential energy curves and transition moments are presented for the ground, excited and Rydberg Σ, Π and Δ states of Na+ 2 up to the Na(7i) + Na+ dissociation limit. The accuracy of the first excited states is checked by comparing with available experimental data. Figures are presented for the molecular quantum defects as a function of internuclear distance, showing an interesting pattern of pseudo-crossings.

Multiphoton studies of jet-cooled Xe2 near the Xe*5d[5/2]3 state: Characterization of the ground and excited state potential curves

The two-photon resonant, three-photon (2+1) ionization spectra of jet-cooled mXenXe, at energies near the Xe* 5d[5/2]03 state, are reported. A new progression has been observed and is attributed to transitions from the van der Waals ground state, X 1Σ+g(0+g), through bound vibrational levels of an excited state of gerade symmetry. The analysis of some 26 closely spaced vibronic bands and isotope effects provides information on the excited and ground state potential energy curves. The vibrational quantum number of the lowest frequency band near 82 539.1 cm−1 is assigned to v′=6±1. For v′=6 this leads to molecular constants Te′ ≂ 82 514.9 cm−1, ωe′ ≂ 5.7955 cm−1, and ωexe′ ≂ 0.07491 cm−1. The upper state can be described by a Morse potential with dissociation energy De′ ≂ 112.10 ± 0.05 cm−1 and internuclear separation Re′ ≂ 5.51 ± 0.03 Å. This is consistent with assignment to a Rydberg molecular state of either the B 2Π1/2g or D 2Σ+1/2g ion core. At the Xe 1S0+Xe* 5d[5/2]03 threshold the molecular spectrum terminates and continuum absorption is evidenced by a rise and fall in the fragment ion yield. The direct determination of the dissociation limit for the excited state is used to derive the ground state dissociation energy De″≂ 196.32 ± 0.05 cm−1.

PHOTOISOMERIZATION OF SIXTEEN ISOMERS OF RETINAL. INITIAL PRODUCT DISTRIBUTION IN DIRECT AND SENSITIZED IRRADIATION. PHOTOCHEMISTRY OF POLYENES 31*

Abstract— Initial product distributions of all 16 geometric isomers of retinal in hexane solutions have been determined. With direct irradiation, the product ratios are characterized by a preference for isomerization at the 13,14‐bond. In particular, all isomers containing the 13‐cis geometry give the corresponding 13‐trans isomer as the major product. Preference for one‐photon‐one‐bond isomerization was also noted, although a substantial amount of the all‐trans isomer was detected for all poly‐cis, 13‐trans isomers. In sensitized irradiation, the initial mixture shows extensive one‐photon‐two(or multiple)‐bond isomerization to the corresponding unhindered isomers. In cases of hindered isomers, multiple‐bond isomerized products are dominant. The different results are accountable by the different shapes of the excited state potential curves for singlet and triplet states.

Hyperspherical formulation of impurity-bound excitons in semiconductors.

A hyperspherical formalism is shown to be an appropriate approach for the investigation of the three-particle complex corresponding to an exciton bound to a Coulomb center in a semiconductor. The ground- and excited-state potential curves and binding energies are calculated as a function of the mass ratio of the hole and electron, and the concept of a critical mass is discussed. The results that we have obtained are in very good agreement with variational calculations for several semiconductor materials.

Ab-initio multiple reference double-excitation configuration-interaction ground and excited state potential curves for the H 2NNO 2 decomposition in nitramine

The H 2NNO 2 decomposition of nitramine is a prototype reaction for a bond decomposition in many energetic species. The relatively small size of the molecule allows theoretical study with high level of sophistication. Large basis set multiple reference double-excitation configuration-interaction (MRD-CI) calculation for the lowest several singlet and triplet potential curves for H 2NNO 2 are presented. A geometry for the ground state has been optimized at the multiconfiguration self-consistent field (MC-SCF) level.

A b i n i t i o multiple reference double-excitation configuration-interaction ground and excited state potential curves for nitromethane decomposition

Reliable ab initio quantum chemical calculations for the ground and electronically excited potential energy surfaces for C–NO2 bond dissociation pathways in addition to the bond dissociation energy from the ground electronic state are crucial to evaluating energetic materials. The excited electronic state potential energy surfaces are important especially for laser induced decomposition. The curve crossings and avoided crossings are important since they determine the electronic states of the resulting fragments which influences their subsequent reactivities. We have carried out large basis set multiple reference double-excitation configuration-interaction (MRD-CI) calculations for the lowest several singlet and triplet potential curves for the H3C – NO2 decomposition of nitromethane. The proper ground state decomposition should lead to two radicals. The self-consistent-field (SCF) treatment (for the ground electronic state) was found to be satisfactory around the equilibrium structure (except for the ever-present ππ* transition of the electrons in the NO2 group) while failing completely to predict the proper dissociation limit. The analysis of the MRD-CI wave function allows distinguishing of two regions which can be interpreted as interaction within bonded molecule and interaction between species of already dissociated molecule.