State Potential Energy Curves Research Articles

Quantum Information Orbitals (QIO): Unveiling Intrinsic Many-Body Complexity by Compressing Single-Body Triviality.

The simultaneous treatment of static and dynamic correlations in strongly correlated electron systems is a critical challenge. In particular, finding a universal scheme for identifying a single-particle orbital basis that minimizes the representational complexity of the many-body wave function is a formidable and longstanding problem. As a contribution toward its solution, we show that the total orbital correlation actually reveals and quantifies the intrinsic complexity of the wave function, once it is minimized via orbital rotations. To demonstrate the power of this concept in practice, an iterative scheme is proposed to optimize the orbitals by minimizing the total orbital correlation calculated by the tailored coupled cluster singles and doubles (TCCSD) ansatz. The optimized orbitals enable the limited TCCSD ansatz to capture more nontrivial information on the many-body wave function, indicated by the improved wave function and energy. An initial application of this scheme shows great improvement of TCCSD in predicting the singlet ground state potential energy curves of the strongly correlated C2 and Cr2 molecule.

Different functional groups dependent fluorescent properties for ESIPT-based ABTN derivatives: A theoretical study

On the basis of density functional theory (DFT) and time-dependent DFT (TD-DFT), 2-amino-3-(benzo[d]thiazol-2-yl)benzaldehyde derivatives (ABTN-1, ABTN-2, ABTN-3) are selected as models to theoretically explore the effect of different functional groups on the fluorescent properties and excited state intramolecular proton transfer (ESIPT) behavior. The optimized configurations, infrared vibrational frequencies and topological parameters are used to analyze the intensity of intramolecular hydrogen bond (IHB). The absorption and fluorescence emission spectra are simulated, and the frontier molecular orbital as well as electron-hole distribution are investigated. In addition, the ground state (S0) and excited state (S1) potential energy curves (PECs) are constructed. The–CN group has little effect on the absorption and fluorescence wavelengths of ABTN. The –N(CH3)2 group red-shifts the absorption and fluorescence wavelengths exceeding 100 nm. The coexistence of –CN and –N(CH3)2 groups has almost the same effect on the absorption and fluorescence peaks as the–N(CH3)2 group.

Which Options Exist for NISQ-Friendly Linear Response Formulations?

Linear response (LR) theory is a powerful tool in classic quantum chemistry crucial to understanding photoinduced processes in chemistry and biology. However, performing simulations for large systems and in the case of strong electron correlation remains challenging. Quantum computers are poised to facilitate the simulation of such systems, and recently, a quantum linear response formulation (qLR) was introduced [Kumar et al., J. Chem. Theory Comput. 2023, 19, 9136-9150]. To apply qLR to near-term quantum computers beyond a minimal basis set, we here introduce a resource-efficient qLR theory, using a truncated active-space version of the multiconfigurational self-consistent field LR ansatz. Therein, we investigate eight different near-term qLR formalisms that utilize novel operator transformations that allow the qLR equations to be performed on near-term hardware. Simulating excited state potential energy curves and absorption spectra for various test cases, we identify two promising candidates, dubbed "proj LRSD" and "all-proj LRSD".

A Study of NbMo and NbMo- by Anion Photoelectron Spectroscopy.

Photoelectron spectra of the niobium-molybdenum diatomic anion, obtained at 488 and 514 nm, display vibrationally resolved transitions from the ground state and one excited electronic state of the anion to the ground state and one excited electronic state of the neutral molecule. The electron affinity of NbMo is measured to be 1.130 ± 0.005 eV. Its 2Δ3/2 spin-orbit component is observed to lie 870 ± 20 cm-1 above its previously identified 2Δ5/2 ground state. For 93Nb98Mo, vibrational energies measured for levels up to v = 4 for the 2Δ5/2 and 2Δ3/2 states give harmonic frequency and anharmonicity constant values of ωe = 492 ± 12 cm-1 and ωexe = 8.0 ± 3.2 cm-1, the former value corresponding to a force constant of 6.80 ± 0.35 mdyn/Å. These two vibrational parameters suggest a bond dissociation energy that is too low by at least a factor of 3, indicating that the ground state potential energy curve of NbMo deviates markedly from a Morse potential at higher energies. An excited electronic state of NbMo, assigned as a 2Σ+ state, is observed at 2900 ± 25 cm-1 (T0). Vibrational energies up to v = 8 in this excited state give values of ωe = 544 ± 8 cm-1 and ωexe = 1.9 ± 1.2 cm-1 for 93Nb98Mo. The former value corresponds to a high vibrational force constant of 8.30 ± 0.25 mdyn/Å. Both doublet states of the neutral molecule are accessed from the anion ground state, which is assigned as 1Σ+. For the 93Nb98Mo- anion, the fundamental vibrational frequency (ΔG1/2) is 484 ± 15 cm-1. Electron affinity data indicate that the bond dissociation energy of NbMo- is 0.213 ± 0.005 eV greater than that of neutral NbMo, whose previously reported value then gives D0 = 4.85 ± 0.27 eV for the anion. An excited state of the anion lying 3050 ± 25 cm-1 (T0) above its ground state is assigned as 3Δ, and the energies of its spin-orbit components above the 3Δ3 lowest energy level are measured to be 450 ± 20 cm-1 (3Δ2) and 1100 ± 20 cm-1 (3Δ1). Their uneven spacing suggests that the energy of the 3Δ2 level is lowered by interaction with a higher energy Ω = 2 anion state. The vibrational frequency (ΔG1/2) for the 3Δ1 and 3Δ2 states is measured to be 433 ± 20 cm-1. Bond length differences among the observed states are estimated from Franck-Condon fits to vibrational band intensity profiles. When combined with the previously reported NbMo bond length, these provide bond length estimates for the ground state of the anion (1.940 ± 0.025 Å) and for the observed excited states. These species offer extreme examples of multiple metal-metal bonding, with formal bond orders of 51/2 for the 2Δ ground and 2Σ+ excited doublet states of NbMo, 6 for the singlet ground state of the anion, and 5 for its low-lying triplet state. The relationships among their bonding properties and those of related multiply bonded transition metal dimers are discussed.

Exploration of interlacing and avoided crossings in a manifold of potential energy curves by a unitary group adapted state specific multi-reference perturbation theory (UGA-SSMRPT).

The Unitary Group Adapted State-Specific Multi-Reference Perturbation Theory (UGA-SSMRPT2) developed by Mukherjee et al. [J. Comput. Chem. 36, 670 (2015)] has successfully realized the goal of studying bond dissociation in a numerically stable, spin-preserving, and size-consistent manner. We explore and analyze here the efficacy of the UGA-SSMRPT2 theory in the description of the avoided crossings and interlacings between a manifold of potential energy curves for states belonging to the same space-spin symmetry. Three different aspects of UGA-SSMRPT2 have been studied: (a) We introduce and develop the most rigorous version of UGA-SSMRPT2 that emerges from the rigorous version of UGA-SSMRCC utilizing a linearly independent virtual manifold; we call this the "projection" version of UGA-SSMRPT2 (UGA-SSMRPT2 scheme P). We compare and contrast this approach with our earlier formulation that used extra sufficiency conditions via amplitude equations (UGA-SSMRPT2 scheme A). (b) We present the results for a variety of electronic states of a set of molecules, which display the striking accuracy of both the two versions of UGA-SSMRPT2 with respect to three different situations involving weakly avoided crossings, moderate/strongly avoided crossings, and interlacing in a manifold of potential energy curves (PECs) of the same symmetry. Accuracy of our results has been benchmarked against IC-MRCISD + Q.

Spontaneous electron emission vs dissociation in internally hot silver dimer anions.

Referring to a recent experiment, we theoretically study the process of a two-channel decay of the diatomic silver anion (Ag2 -), namely, the spontaneous electron ejection giving Ag2 + e- and the dissociation leading to Ag- + Ag. The ground state potential energy curves of the silver molecules of diatomic neutral and negative ions were calculated using proper pseudo-potentials and atomic basis sets. We also estimated the non-adiabatic electronic coupling between the ground state of Ag2 - and the ground state of Ag2 + e-, which, in turn, allowed us to estimate the minimal and mean values of the electron autodetachment lifetimes. The relative energies of the rovibrational levels allow the description of the spontaneous electron emission process, while the description of the rotational dissociation is treated with the quantum dynamics method as well as time-independent methods. The results of our calculations are verified by comparison with the experimental data.

Dissociation dynamics of multiply charged CH3I in moderately intense laser fields

We report on the fragmentation of multiply charged ${\mathrm{CH}}_{3}\mathrm{I}$ ions through dissociative ionization and Coulomb explosion induced by moderately intense (${10}^{12}--{10}^{13} \mathrm{W}/{\mathrm{cm}}^{2}$) ultrashort laser fields. Velocity map imaging of the fragment ions as a function of pulse duration, ranging from 25 fs to 1.5 ps, leads to kinetic energies, angular distributions, and the relative ion yield in different channels of these fragments. We propose possible pathways for the fragmentation channels based on the kinetic energies and theoretical potential energy curves. For the energetic fragments, we observe an enhanced yield with increasing pulse duration. A simple one-dimensional classical model of wave-packet propagation over the proposed intermediate state potential energy curve is used to estimate the ionization probability as a function of pulse duration. Our results suggest that a delayed enhanced ionization is a consequence of rearrangement of the energies of the molecular orbitals following bond stretching. The resultant energy upshift of the inner orbitals at larger internuclear separation gives rise to resonant multiorbital coupling at a critical distance, which enables enhanced ionization for longer pulses.

Mechanism of 2, 3-difurylmaleic anhydride photochromic molecular switch

The photochromic switching mechanism of 2,3-difurylmaleic anhydride (DFMA) is investigated by first-principles calculations. Based on the stable structures of the open-ring (O-DFMA) and closed-ring (C-DFMA) of the DFMA, the minimum energy path (MEP) and the configuration of transition states (TS-DFMA) between the O-DFMA and C-DFMA are found by using the nudged elastic band (NEB) method, the potential barriers of O-DFMA and C-DFMA are 24959 cm<sup>–1</sup>(3.0945 eV) and 23328 cm<sup>–1</sup>(2.8923 eV), respectively, indicating that the DFMA molecule may be a thermally bistable molecule. Along the molecular configuration corresponding to the MEP curve (i.e. ground state S<sub>0</sub>), the potential energy curves of the lowest 8 singlet excited states of DFMA are calculated. Among these energy curves, only the first electronic excited state (i.e. S<sub>1</sub> state) has a minimum value in the transition state (TS-DFMA) configuration. Combined with the molecular orbital transitions and orbital images, the photochromic mechanism of DFMA can be described as follows (1) From C-DFMA to O-DFMA process: under the action of the laser with S<sub>1</sub>–S<sub>0</sub> resonance transition wavelength, the C-DFMA transits from S<sub>0</sub> to S<sub>1</sub> state, and then deactivates along the S<sub>1</sub> potential energy curve, until a cross jumping transition occurs at the TS-DFMA structure from S<sub>1</sub> to S<sub>0</sub> and finally the molecule along the S<sub>0</sub> potentioal energy curve returns to the O-DFMA configuration, then the switching action from closed-ring to open-ring is completed. The S<sub>1</sub> state potential energy curve drops monotonically in this switching process, implying that there will be no fluorescent radiation in this process. (2) From O-DFMA to C-DFMA process: under the action of the laser with S<sub>1</sub>–S<sub>0</sub> resonance transition wavelength, O-DFMA transits from S<sub>0</sub> to S<sub>1</sub> state. From the O-DFMA to TS-DFMA structure, there is a relatively “flat” area in the potential energy curve of the S<sub>1</sub> state, and it decreases significantly only when it is close to the TS-DFMA. This means that O-DFMA needs to be excited with some vibrational modes to pass through the “flat” region of S<sub>1</sub> and approaching to the TS-DFMA configuration, and then DFMA de-excites from the S<sub>1</sub> state potential energy curve along a monotonic decline and a cross jumping transition from S<sub>1</sub> to S<sub>0</sub> occurs in the TS-DFMA configuration, completing the switching action from open-ring to closed-ring. It is also precisely because of the flat region of the potential energy curve of the initial S<sub>1</sub> state that this excitation and switching process is accompanied by fluorescent radiations. The photochromic mechanism of DFMA indicates that it is suitable for making fluorescent molecular switches.

Hybrid Quantum-Classical Neural Network for Calculating Ground State Energies of Molecules.

We present a hybrid quantum-classical neural network that can be trained to perform electronic structure calculation and generate potential energy curves of simple molecules. The method is based on the combination of parameterized quantum circuits and measurements. With unsupervised training, the neural network can generate electronic potential energy curves based on training at certain bond lengths. To demonstrate the power of the proposed new method, we present the results of using the quantum-classical hybrid neural network to calculate ground state potential energy curves of simple molecules such as H, LiH, and BeH. The results are very accurate and the approach could potentially be used to generate complex molecular potential energy surfaces.

First-principles calculation of excited states of diatomic molecules: a benchmark for the Gutzwiller conjugate gradient minimisation method

We recently proposed the Gutzwiller conjugate gradient minimisation (GCGM) method for efficient and accurate calculation of the ground state total energy of molecular and bulk systems. The GCGM method is developed under the framework of Gutzwiller wave function but goes beyond the commonly adopted Gutzwiller approximation to improve the accuracy and flexibility in treating the correlation effects. In this conference proceeding, we benchmark the GCGM method with the calculation of excited state potential energy curves of three diatomic molecules, namely H2, N2, and O2. Our calculations demonstrate the flexibility and reasonable accuracy of the method.

Comprehending the quadruple bonding conundrum in C2 from excited state potential energy curves

The question of quadruple bonding in C2 has emerged as a hot button issue, with opinions sharply divided between the practitioners of Valence Bond (VB) and Molecular Orbital (MO) theory. Here, we have systematically studied the Potential Energy Curves (PECs) of low lying high spin sigma states of C2, N2, Be2 and HC[triple bond, length as m-dash]CH using several MO based techniques such as CASSCF, RASSCF and MRCI. The analyses of the PECs for the 2S+1Σg/u (with 2S + 1 = 1, 3, 5, 7, 9) states of C2 and comparisons with those of relevant dimers and the respective wavefunctions were conducted. We contend that unlike in the case of N2 and HC[triple bond, length as m-dash]CH, the presence of a deep minimum in the 7Σ+ state of C2 and CN+ suggests a latent quadruple bonding nature in these two dimers. Our investigations reveal that the number of bonds in the ground state can be determined for 2nd row dimers by figuring out at what value of spin symmetry a purely dissociative PEC is obtained. For N2 and HC[triple bond, length as m-dash]CH the purely dissociative PEC appears for the septet spin symmetry as compared to that for the nonet in C2. This is indicative of a higher number of bonds between the two 2nd row atoms in C2 as compared to those of N2 and HC[triple bond, length as m-dash]CH. Hence, we have struck a reconciliatory note between the MO and VB approaches. The evidence provided by us can be experimentally verified, thus providing the window so that the narrative can move beyond theoretical conjectures.

Parametrisation of the optimised effective potential method based on the Coulson–Fischer wave function for excited states

ABSTRACT This article further develops the Coulson–Fischer formalism in conjunction with the optimised effective potential method [V.N. Glushkov and S. Wilson, Molec. Phys. 110, 149 (2012)] to incorporate both exchange and static correlation effects for excited states having the same symmetry as the ground state. By using this formalism, we compute complete potential energy curves for the ground and first excited states of the molecule and the isoelectronic heteronuclear ion. Effective potentials are generated in according to a novel density functional theory [A.K. Theophilou, J. Chem. Phys. 149, 074104 (2018)] in which the Kohn–Sham (KS) like potential has spherical symmetry around each nucleus. In this way, the inconsistencies of standard density functional theory concerning the asymmetry of the KS potential are remedied. In our implementation, an effective potential which satisfies this requirement is expressed as a direct mapping of the external potential. Different approximations for the effective potentials are investigated. It is shown that applications of the proposed formalism support good agreement with the exact Coulson–Fischer theory for both the ground and first excited state potential energy curves and thus a qualitatively correct description of dissociation.

Determination of the C(3)1Σ+ state potential energy curve in KCs molecule based on polarisation labelling spectroscopy data

The C(3)1Σ+ state of KCs molecule was studied experimentally employing the polarisation labelling spectroscopy (PLS) technique. The experiment extended the prior knowledge of the state adding more than 40 vibrational levels to the previously existing data. A pointwise potential energy curve was constructed for the investigated state with the inverted perturbation approach (IPA) method, basing on experimentally determined energies of over 1300 rovibrational levels.

Speed tunability of the excited-state intramolecular proton transfer process based on seven-membered ring pyrrole-indole H-bond systems

A speed tunable excited-state intramolecular proton transfer (ESIPT) system featuring a seven-membered ring, -NH- type hydrogen bonding pyrrole-indole moiety based on ‘naked’ diazaborepins (NDABs) was exhibited. In this paper, the speed of ESIPT process can be tuned by the substituents on indole ring, including electron donating and withdrawing group for NDAB-H, NDAB-OMe, NDAB-COOEt, NDAB-NEt2, NDAB-CF3. It has explained by DFT and TD-DFT calculation in nonpolar toluene. The energy gaps between NS1 and TS1 (△E = ET-S1 − EN-S1) of most NDABs are slightly positive, except for the energy gap of NDAB-NEt2 with strong donating group on indole ring is negative. Meanwhile, the S1 state potential energy curve of NDABs with a small energy barrier is in the order NDAB-NEt2 < NDAB-OMe ~ NDAB-H < NDAB-COOEt < NDAB-CF3. Therefore, it indicates that ESIPT reaction could happen on the NDABs system. Strong withdrawing groups on indole ring of NDABs could restrain the ESIPT process and strong donating groups could promote the ESIPT process, which is in good agreement with the corresponding Stokes shift between absorption and emission spectra in N and/or T tautomer experimentally. The ESIPT process of NDABs in polar aprotic DMSO by the same calculation method also has been certified.

A DFT/TDDFT Investigation of Excited State Dynamical Mechanism of (E)‐1‐((2,2‐Diphenylhydrazono)methyl)naphthalen‐2‐ol

The excited‐state intramolecular proton transfer (ESIPT) mechanism of a new compound (E)‐1‐((2,2‐diphenylhydrazono)methyl)naphthalen‐2‐ol (EDMN) sensor, reported and synthesized by Mukherjee et al. [Sensors Actuat. B‐Chem. 2014, 202, 1190], is investigated in detail theoretically. The calculations on primary bond lengths, bond angles, and the corresponding infrared (IR) vibrational spectra and hydrogen‐bond energy involved in intramolecular hydrogen bond between the S0 and S1 states confirm that the intramolecular hydrogen bond is strengthened in the S1 state, which reveals the tendency of ESIPT reaction. The fact that the experimental absorption and emission spectra are well reproduced demonstrates the rationality and effectiveness of the time‐dependent density functional theory (TDDFT) level of theory we adopt here. Furthermore, intramolecular charge transfer based on the frontier molecular orbitals (MOs) gives indication of the ESIPT reaction. The constructed potential energy curves of both the S0 and S1 states while keeping the O─H distance of EDMN fixed at a series of values are used to illustrate the ESIPT process. The lower barrier of ~3.934 kcal/mol in the S1 state potential energy curve (lower than the 8.254 kcal/mol in the S0 state) provides the transfer mechanism.

A Jeziorski-Monkhorst fully uncontracted multi-reference perturbative treatment. I. Principles, second-order versions, and tests on ground state potential energy curves.

The present paper introduces a new multi-reference perturbation approach developed at second order, based on a Jeziorski-Mokhorst expansion using individual Slater determinants as perturbers. Thanks to this choice of perturbers, an effective Hamiltonian may be built, allowing for the dressing of the Hamiltonian matrix within the reference space, assumed here to be a CAS-CI. Such a formulation accounts then for the coupling between the static and dynamic correlation effects. With our new definition of zeroth-order energies, these two approaches are strictly size-extensive provided that local orbitals are used, as numerically illustrated here and formally demonstrated in the Appendix. Also, the present formalism allows for the factorization of all double excitation operators, just as in internally contracted approaches, strongly reducing the computational cost of these two approaches with respect to other determinant-based perturbation theories. The accuracy of these methods has been investigated on ground-state potential curves up to full dissociation limits for a set of six molecules involving single, double, and triple bond breaking together with an excited state calculation. The spectroscopic constants obtained with the present methods are found to be in very good agreement with the full configuration interaction results. As the present formalism does not use any parameter or numerically unstable operation, the curves obtained with the two methods are smooth all along the dissociation path.

Alternative definition of excitation amplitudes in multi-reference state-specific coupled cluster.

A central difficulty of state-specific Multi-Reference Coupled Cluster (MR-CC) in the multi-exponential Jeziorski-Monkhorst formalism concerns the definition of the amplitudes of the single and double excitation operators appearing in the exponential wave operators. If the reference space is a complete active space (CAS), the number of these amplitudes is larger than the number of singly and doubly excited determinants on which one may project the eigenequation, and one must impose additional conditions. The present work first defines a state-specific reference-independent operator T∼^m which acting on the CAS component of the wave function |Ψ0m⟩ maximizes the overlap between (1+T∼^m)|Ψ0m⟩ and the eigenvector of the CAS-SD (Singles and Doubles) Configuration Interaction (CI) matrix |ΨCAS-SDm⟩. This operator may be used to generate approximate coefficients of the triples and quadruples, and a dressing of the CAS-SD CI matrix, according to the intermediate Hamiltonian formalism. The process may be iterated to convergence. As a refinement towards a strict coupled cluster formalism, one may exploit reference-independent amplitudes provided by (1+T∼^m)|Ψ0m⟩ to define a reference-dependent operator T^m by fitting the eigenvector of the (dressed) CAS-SD CI matrix. The two variants, which are internally uncontracted, give rather similar results. The new MR-CC version has been tested on the ground state potential energy curves of 6 molecules (up to triple-bond breaking) and two excited states. The non-parallelism error with respect to the full-CI curves is of the order of 1 mEh.

Theoretical study of excited state intramolecular proton transfer (ESIPT) mechanism for a fluorophore in the polar and nonpolar solvents

2, 4-dibenzothiazolyl-phenol (2, 4-DBTP), a fluorophore developing induced emission properties, undergoes excited state intramolecular proton transfer (ESIPT) taking place along its strong hydrogen bond. 2,4-DBTP has been investigated in the polar and nonpolar solvents by means of time-dependent density functional theory (TDDFT). The TDDFT absorption and emission wavelengths obtained through the vertical approximation are in good agreement with their experimental counterparts, confirming the existence of an ESIPT process and indicating that the selected level of theory is reasonable. Hydrogen bond strengthening has been testified in the S1 state based on comparing primary bond lengths and bond angles involved in the intramolecular hydrogen bond between the S0 and S1 state. Furthermore, the frontier molecular orbitals (MOs) analysis method manifest the intramolecular charge transfer, which reveals the tendency of ESIPT process. To further characterize the ESIPT process, we determined the potential-energy curves of the S0 and S1 states.Compared with 2,4-DBTP monomer, the S1 state potential energy curve of 2,4-DBTP-MeOH complex has a bigger slope with no potential barrier. Therefore, we can indicate that the ESIPT process for 2,4-DBTP is much easier in methanol solvent.

Photoinduced C—I bond homolysis of 5-iodouracil: A singlet predissociation pathway

5-Iodouracil (5-IU) can be integrated into DNA and acts as a UV sensitive chromophore suitable for probing DNA structure and DNA-protein interactions based on the photochemical reactions of 5-IU. Here, we perform joint studies of time-resolved Fourier transform infrared (TR-FTIR) spectroscopy and ab initio calculations to examine the state-specific photochemical reaction mechanisms of the 5-IU. The fact that uracil (U) is observed in TR-FTIR spectra after 266 nm irradiation of 5-IU in acetonitrile and ascribed to the product of hydrogen abstraction by the uracil-5-yl radical (U·) provides experimental evidence for the C-I bond homolysis of 5-IU. The excited state potential energy curves are calculated with the complete active space second-order perturbation//complete active space self-consistent field method, from which a singlet predissociation mechanism is elucidated. It is shown that the initially populated 1(ππ*) state crosses with the repulsive 1(πσ*) or 1(nIσ*) state, through which 5-IU undergoes dissociation to the fragments of (U·) radical and iodine atom. In addition, the possibility of intersystem crossing (ISC) is evaluated based on the calculated vertical excitation energies. Although a probable ISC from 1(ππ*) state to 3(nOπ*) and then to the lowest triplet 3(ππ*) could occur in principal, there is little possibility for the excited state populations bifurcating to triplet manifold, given that the singlet state predissociation follows repulsive potential and should occur within dozens to hundreds of femtoseconds. Such low population of triplet states means that the contribution of triplet state to photoreactions of 5-IU should be quite minor. These results demonstrate clearly a physical picture of C-I bond homolysis of 5-IU and provide mechanistic illuminations to the interesting applications of 5-IU as photoprobes and in radiotherapy of cancer.

Metastable homonuclear diatomic trications [formula omitted] for elements X from the first three rows of the periodic table

Motivated by a systematic stability scan of the homonuclear diatomic systems with elements from hydrogen to argon, we investigated in detail the ensuing five candidates for metastable trications, viz., O23+, P23+, S23+, Cl23+, and Ar23+ by multireference configuration interaction computations. Each of these tricationic systems exhibits a barrier in its ground state potential energy curve leading to quasi-bound nuclear motion. The resulting lifetimes vary drastically; while S23+ and Cl23+ in their lowest vibrational states can be regarded as practically stable, the predicted lifetimes of O23+ and Ar23+ are too short to allow a mass spectroscopic detection of these systems by current experimental capabilities. In the case of Ar23+, the theoretically predicted existence of quasibound vibrational levels also depends on whether or not relativistic corrections are taken into account.