Dissociation Limit Research Articles

Ab initioand analytical studies of the spin-orbit coupling in heteronuclear alkali-metal dimersAB(A, B= Li, Na, K, Rb) at long ranges

The spin-orbit (SO) coupling matrix elements between the excited states of the lightest heteronuclear alkali metal dimers AB(A, B = Li, Na, K, Rb) converging to the first three dissociation limits were evaluated by employing the quasirelativistic electronic wave functions in a wide range of interatomic distances, $R$. The inner-shell electrons of alkali atoms were described using nonempirical shape-consistent effective core potentials. To take the core-valence correlation effects into account, core polarization potentials for each atom were implemented. Dynamical correlation was introduced through the multireference configuration interaction method, which was applied to two valence electrons keeping all subvalence electrons frozen. The reliability of the derived SO functions is accessed through comparison, wherever possible, with their preceding theoretical and experimental counterparts. The ab initio SO matrix elements were approximated beyond the LeRoy radius using the formula: ${\ensuremath{\xi}}_{if}^{\text{SO}}(R)=\ensuremath{\alpha}+{\ensuremath{\beta}}_{if}^{[k]}/{R}^{k}$, where (1) $k=6$ and $\ensuremath{\alpha}={\ensuremath{\xi}}_{n^{2}\mathrm{P}}^{\text{SO}}$ is the SO splitting of the atom $\mathrm{A}(n^{2}\mathrm{P}$) for the states of the AB molecule converging to the same $\mathrm{A}({n}_{\mathrm{A}}^{2}\mathrm{P}$) + $\mathrm{B}({n}_{\mathrm{B}}^{2}\mathrm{S}$) dissociation limit, and (2) $k=3$ and $\ensuremath{\alpha}=0$ for the molecular $i$ and $f$ states converging to the $\mathrm{A}({n}_{\mathrm{A}}^{2}\mathrm{P})+\mathrm{B}({n}_{\mathrm{B}}^{2}\mathrm{S})$ and $\mathrm{A}({n}_{\mathrm{A}}^{2}\mathrm{S})+\mathrm{B}({n}_{\mathrm{B}}^{2}\mathrm{P}$) atomic thresholds, respectively. A theoretical justification of these formulas was derived from the multipole expansion of the molecular SO operator in terms of the inverse powers of the internuclear distance and of products of operators acting on the electronic coordinates of the atoms A and B.

Climbing vibrational levels

Chemical Physics Vibrational excitation of molecules adsorbed on a surface is usually limited because the vibrational energy is rapidly transferred into phonons, the vibrational modes of the substrate. Chen et al. found that this is not the case for CO molecules adsorbed on a surface of NaCl. The CO molecules efficiently transferred vibrational energy within groups of molecules from one high excitation state to another until they reached the dissociation limit. This process was possible because of the close proximity of the molecules and the limited transfer of energy to just one phonon mode in the salt surface. Science , this issue p. [158][1] [1]: /lookup/doi/10.1126/science.aav4278

Observation of the shallow state of NaH.

The 2 1Π state of NaH has been observed up to the last bound vibrational level using pulsed optical-optical double resonance fluorescence depletion spectroscopy. A total of 20 rovibrational energy levels ( = 2-4 and J = 1-9) were assigned to this electronic state by means of comparing the successive rovibrational spectra to the eigenvalues of the ab initio potential energy curve. The decrease of background fluorescence near the atomic asymptotic limit Na(3d) + H(1s) is an indication of reaching the dissociation limit of the NaH 2 1Π state. Unobserved rovibrational levels ( = 0 and 1) are due to poor Franck-Condon overlap of 2 1Π ← A 1Σ+ transition within the accessible rovibrational levels of intermediate A 1Σ+ state of this work.

Radiative transition probabilities between low-lying electronic states of N2

ABSTRACTThis work mainly investigates the transition dipole moments (TDMs) and radiative transition probabilities of dipole-allowed transitions between the , , , , , , , , and states of N2. Many of these transition properties are previously unknown. For completeness, another 14 electronic states that correlate to four lowest dissociation limits are also calculated. The potential energy curves (PECs) are calculated at the valence internally contracted multireference configuration-interaction (icMRCI) level of theory, along with the Davidson correction, the core-valence (CV) correction and the scalar relativistic correction, as well as the basis-set extrapolation. These corrections, especially the CV correction, greatly improve the accuracy of the PECs, as shown by the excellent agreement of the fitted spectroscopic parameters with the available experimental data. In order to verify the accuracy of transition properties, we calculate the Einstein coefficients of the extensively studied band transition systems and compute the radiative lifetimes of states, which are in good agreement with the experimental data. Similar accuracy can be assumed for the previously undetermined band transition systems. The large Einstein coefficients of these band systems can provide guidelines for observing such newly predicted band transitions in the appropriate spectroscopy experiments.

The interparticle distance limit for multiple exciton dissociation in PbS quantum dot solid films.

Understanding the behaviour of multiple exciton dissociation in quantum dot (QD) solid films is of fundamental interest and paramount importance for improving the performance of quantum dot solar cells (QDSCs). Unfortunately, the charge transfer behaviour of photogenerated multiple exciton in QD solid films is not clear to date. Herein, we systematically investigate the multiple exciton charge transfer behaviour in PbS QD solid films by using ultrafast transient absorption spectroscopy. We observe that the multiple exciton charge transfer rate within QD ensembles is exponentially enhanced as the interparticle distance between the QDs decreases. Biexciton and triexciton dissociation between adjacent QDs occurs via a charge transfer tunneling effect just like single exciton, and the charge tunneling constants of the single exciton (β1: 0.67 ± 0.02 nm-1), biexciton (β2: 0.68 ± 0.05 nm-1) and triexciton (β3: 0.71 ± 0.01 nm-1) are obtained. More importantly, for the first time, the interparticle distance limit (≤4.3 nm) for multiple exciton charge transfer between adjacent QDs is found for the extraction of multiple excitons rapidly before the occurrence of Auger recombination. This result points out a vital and necessary condition for the use of multiple excitons produced in PbS QD films, especially for their applications in QDSCs.

Electronic and vibrational spectroscopy of the low-lying states of potassium mono-sulphide KS, and comparison in the series of MS (M = Li, Na, K, Rb, Cs)

ABSTRACTPotential energy curves (PECs) of the lowest electronic states of the potassium mono-sulphide KS have been determined with highly correlated ab initio calculations, using internally contracted multi reference interaction configuration methods including Davidson correction (MRCI + Q) with and without considering spin-orbit effects. For the three low-lying bound states, we report a set of spectroscopic parameters including equilibrium distances, dissociation energies, vibrational and rotational constants. The effects of spin-orbit-induced changes on these parameters are also discussed. An analysis of the properties of the three bound states, X2Π, 12Σ+ and 22Π, illustrates the common characteristics of the whole series of compounds in the MS family (M = Li, Na, K, Rb, Cs). Indeed, the shapes of the PECs of these bound states are strongly affected by the interactions between the two ionic states, 2Σ+ and 2Π, correlating at large internuclear separations (RMS) to the first ionic dissociation limit [M+ + S−] and the electronic states correlating to the three/four lowest dissociation limits. The spectroscopy of these low-lying electronic states and the lifetime of their vibrational levels are thus affected by the spin-orbit interactions which are mainly related to the S atom and consequently common to all alkali-metal mono-sulphides.

Solving the Schrödinger equation of hydrogen molecule with the free complement-local Schrödinger equation method: Potential energy curves of the ground and singly excited singlet and triplet states, Σ, Π, Δ, and Φ.

The free-complement (FC) theory for solving the Schrödinger equation (SE) was applied to calculate the potential energy curves of the ground and excited states of the hydrogen molecule (H2) with the 1Σg +, 1Σu +, 3Σg +, 3Σu +, 1Πg, 1Πu, 3Πg, 3Πu, 1Δg, 1Δu, 3Δg, 3Δu, 1Φg, 1Φu, 3Φg, and 3Φu symmetries (in total, 54 states). The initial functions of the FC theory were formulated based on the atomic states of the hydrogen atom and its positive and negative ions at the dissociation limits. The local Schrödinger equation (LSE) method, which is a simple sampling-type integral-free methodology, was employed instead of the ordinary variational method and highly accurate results were obtained stably and smoothly along the potential energy curves. Thus, with the FC-LSE method, we succeeded to perform the comprehensive studies of the H2 molecule from the ground to excited states belonging up to higher angular momentum symmetries and from equilibriums to dissociation limits with almost satisfying spectroscopic accuracy, i.e., 10-6 hartree order around 1 cm-1, as absolute solutions of the SE by moderately small calculations.

Highly sensitive photoassociation spectroscopy of ultracold 23Na133Cs molecular long-range states below the 3S1/2+6P1/2 limit

This article describes the preparation of ultracold heteronuclear polar excited NaCs molecules through photoassociation in a dual-species magneto-optical trap. Ten resonant positions are observed below the Na (3S1/2) + Cs (6P1/2) dissociation limit using trap-loss spectroscopy based on a highly sensitive modulation technique. We deduce the long-range molecular coefficients by fitting an improved LeRoy–Bernstein formula to our experimental data using the Levenberg–Marquardt algorithm implemented in Mathematica software, and derive the empirical potential energy curve in the long-range region; we also verify the application of the improved LeRoy–Bernstein formula to the ultracold NaCs molecule.

The Sommerfeld ground-wave limit for a molecule adsorbed at a surface.

Using a mid-infrared emission spectrometer based on a superconducting nanowire single-photon detector, we observed the dynamics of vibrational energy pooling of carbon monoxide (CO) adsorbed at the surface of a sodium chloride (NaCl) crystal. After exciting a majority of the CO molecules to their first vibrationally excited state (v = 1), we observed infrared emission from states up to v = 27. Kinetic Monte Carlo simulations showed that vibrational energy collects in a few CO molecules at the expense of those up to eight lattice sites away by selective excitation of NaCl's transverse phonons. The vibrating CO molecules behave like classical oscillating dipoles, losing their energy to NaCl lattice vibrations via the electromagnetic near-field. This is analogous to Sommerfeld's description of radio transmission along Earth's surface by ground waves.

Isotope effect and gerade versus ungerade symmetry in HD predissociation revealed by theH(2s),H(2p),D(2s), andD(2p)fragments

The isotope effect and the $g\ensuremath{-}u$ symmetry in the HD predissociation have been studied by detecting the $\mathrm{H}(2s)$, $\mathrm{H}(2p)$, $\mathrm{D}(2s)$, and $\mathrm{D}(2p)$ fragments. For transitions to the $3p\ensuremath{\pi}D{\phantom{\rule{4pt}{0ex}}}^{1}{\mathrm{\ensuremath{\Pi}}}_{u}^{+}(\ensuremath{\upsilon}=4)$, $4p\ensuremath{\pi}{D}^{\ensuremath{'}}{\phantom{\rule{4pt}{0ex}}}^{1}{\mathrm{\ensuremath{\Pi}}}_{u}^{+}(\ensuremath{\upsilon}=1)$, and $4p\ensuremath{\sigma}{B}^{\ensuremath{'}\ensuremath{'}}{\phantom{\rule{4pt}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+}(\ensuremath{\upsilon}=2)$ states of HD, the branching ratios of the four dissociation channels, $\mathrm{H}(2s)+\mathrm{D}(1s)$, $\mathrm{H}(2p)+\mathrm{D}(1s)$, $\mathrm{D}(2s)+\mathrm{H}(1s)$, and $\mathrm{D}(2p)+\mathrm{H}(1s)$, were measured. Strong asymmetric distributions are found between the $\mathrm{H}(2s)+\mathrm{D}(1s)$ and $\mathrm{D}(2s)+\mathrm{H}(1s)$, and between the $\mathrm{H}(2p)+\mathrm{D}(1s)$ and $\mathrm{D}(2p)+\mathrm{H}(1s)$ channels. The results indicate the existence of $g\ensuremath{-}u$ symmetry breaking as well as strong nonadiabatic couplings near the HD dissociation limits. However, the angular anisotropy parameters are found to be the same for the $\mathrm{H}(2s/2p)$ and $\mathrm{D}(2s/2p)$ fragments. In addition, the observed Beutler-Fano profiles in the $\mathrm{H}(2s/2p)$- and $\mathrm{D}(2s/2p)$-atom action spectra show no dependence on the H and D isotopes. This implies that the angular distribution of the fragments and the Beutler-Fano profiles are determined chiefly by the Franck-Condon transitions and are not affected by the $g\ensuremath{-}u$-state mixing.

Effect of external magnetic field on the shift of resonant frequency in photoassociation of ultracold Cs atoms**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0304203), the Chang Jiang Scholars and Innovative Research Team in the University of the Ministry of Education of China (Grant No. IRT13076), the National Natural Science Foundation of China (Grant

We study the influence of external magnetic field on the shift of the resonant frequency in the photoassociation of ultracold Cs atoms, which are captured in a magnetically levitated optical crossed dipole trap. With the increase of the photoassociation laser intensity, the linear variation of the frequency shift is measured by recording the photoassociation spectra of the long-range state of Cs molecule below the 6S1/2+6P1/2 dissociation limit at different magnetic fields. The slope of the frequency shift to the intensity of the photoassociation laser exhibits a strong dependence on the external magnetic field. The experimental data is simulated with an analytic theory model, in which a single channel rectangular potential with the tunable well depth is introduced to acquire the influence of the magnetic field on the atomic behavior in the effective range where photoassociation occurs.

Development of formalisms based on locally coupled open subsystems for calculations in molecular electronic structure and dynamics

Quantum embedding theories model a collection of interacting molecules as a set of subsystems, where each can be treated with a particular electronic structure method (wave function or density functional theory, for example); these theories can lead to computationally efficient and accurate algorithms. Motivated by challenges in the field, we previously described a formalism (that models two subsystems), which we call ``locally coupled open subsystems'' (LCOS), for the computation of ground-state energies, fractional electron-occupation numbers of the subsystems, and the size-consistent limit of subsystem dissociation. In this work we present the full (nonrelativistic) LCOS theory and the following extensions of our previous work: (i) the framework to study systems composed of multiple subsystems and a procedure to spin-adapt the auxiliary wave function that describes the partitioned system, so that its spin state matches that of the real system of interest; (ii) potential functionals and ideas to employ machine learning for the computation of ground-state densities and energies; (iii) formulation of two LCOS ground-state approaches where the fragments are assigned Kohn-Sham wave functions; and (iv) a time-dependent (TD) extension of these two ground-state formalisms in which the state of the subsystems evolves according to a unitary propagation; from this evolution we can extract TD electron populations of the fragments, for instance. We also discuss potential applications of the TD LCOS theory to linear photoabsorption and Raman spectroscopy. The developments presented in this work can lead to ground-state and TD electronic structure calculations where the computational scaling can be controlled, depending on the level of theory and the accuracy desired to model each one of the subsystems and their coupling.

Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F1 and F2 spin-rotation levels of the CN products.

One of the most spectacular yet unsolved problems for the ICN -band photodissociation is the non-statistical spin-rotation F1 = N + 1/2 and F2 = N - 1/2 populations for each rotation level N of the CN fragment. The F1 /F2 population difference function f(N) exhibits strong N and λ dependences with an oscillatory behavior. Such details were found to critically depend on the number of open-channel product states, namely, whether both I (2 P3/2 ) and I (2 P1/2 ) are energetically available or not as the dissociation partner. First, in the asymptotic region, the exchange and dipole-quadrupole inter-fragment interactions were studied in detail. Then, as the diabatic basis, we took the appropriate symmetry adapted products of the electronic and rotational wavefunctions for the F1 and F2 levels at the dissociation limits. We found that the adiabatic Hamiltonian exhibits Rosen-Zener-Demkov type nonadiabatic transitions reflecting the switch between the exchange interaction and the small but finite spin-rotation interaction within CN at the asymptotic region. This non-crossing type nonadiabatic transition occurs with the probability 1/2, that is, at the diabatic limit through a sudden switch of the quantization axis for CN spin S from the dissociation axis to the CN rotation axis N. We have derived semiclassical formulae for f(N) and the orientation parameters with a two-state model including the 3A' and 4A' electronic states, and with a four-state model including the 3A' through 6A' electronic states. These two kinds of interfering models explain general features of the F1 and F2 level populations observed by Zare's group and Hall's group, respectively. © 2018 Wiley Periodicals, Inc.

Fermi-Löwdin orbital self-interaction corrected density functional theory: Ionization potentials and enthalpies of formation.

The Fermi-Löwdin orbital self-interaction correction (FLO-SIC) methodology is applied to atoms and molecules from the standard G2-1 test set. For the first time FLO-SIC results for the GGA-type PBE functional are presented. In addition, examples where FLO-SIC like any proper SIC provides qualitative improvements compared to standard DFT functionals are discussed in detail: the dissociation limit for , the step-wise linearity behavior for fractional occupation, as well as the significant reduction of the error of static polarizabilities. Further, ionization potentials and enthalpies of formation obtained by means of the FLO-SIC DFT method are compared to other SIC variants and experimental values. The self-interaction correction gives significant improvements if used with the LDA functional but shows worse performance in case of enthalpies of formation if the PBE-GGA functional is used. The errors are analyzed and the importance of the overbinding of hydrogen is discussed. © 2018 Wiley Periodicals, Inc.

Multi reference studies of gas phase vanadium nitride di- and trications

Using ab initio configuration interaction methodologies, we compute the potentials of the doubly and triply charged vanadium nitride. By performing benchmark calculations, we show that the 4s and 3d AOs are enough for the accurate description of VN multiple ionizations. In VN2+, several deep potential wells are located below the lowest dissociation limit. Within these potential wells, long-lived rovibrational levels may be found. Specifically, we find an unconventional shape for the ground state potential of VN2+ that differs from the volcanic form typical of dications. For VN3+, four shallow potential wells were characterized that may support rovibrational levels, where metastable VN3+ can be found. Accordingly, we predict the existence of VN2+ and VN3+ species in the gas phase as already noticed experimentally for the dication VN2+. For the bound states, we provide a set of accurate spectroscopic parameters. Double and triple ionization energies of VN are computed to be 23.56 and 51.05 eV, respectively.

Connecting the Dunham Expansion to the Dissociation Limit for Interatomic Potentials: Application to Lennard-Jones m- n Potentials.

Dunham generated the expansion for energy levels of a rotating, vibrating diatomic molecule from an expansion of the potential about the equilibrium position. For partition functions, however, the energy levels are needed all the way to dissociation. Analytic Morse oscillator energies are not very useful because the exponential decay of the Morse potential is much too short-ranged for any physical system. The longer-range Lennard-Jones 12-6 potential could be used, but quantum energies have not previously been conveniently fit. I show how Dunham coefficients begin a set of asymptotic functions for any interaction potential, one function arising from each successive term in the WKB expansion. I apply this to the family of Lennard-Jones m- n (LJ m- n) potentials with an R-m repulsive term and R-n attractive term ( m > n) and demonstrate how m can be used as a parameter to adjust either the equilibrium distance or harmonic frequency. I present an empirical parametrization of LJ m- n vibrotor energies starting with Dunham coefficients generated from four terms in the WKB expansion. This information is combined with data from numerically solved energies and asymptotic limits to fit the functions all the way to dissociation. One can also treat exp-6 and similar model potentials with different repulsive parts using the same method because the expansion form is controlled by the long-range part of the potential.

Theoretical investigation on the low-lying electronic states of beryllium antimonide.

The Λ-S electronic states with respect to the lowest four dissociation limits of BeSb are investigated theoretically on the icMRCI + Q level employing basis set of quintuple-ζ quality. The geometrical parameters, potential energy curves, vibrational energy levels, spectroscopic constants for the twelve Λ - S states are obtained, analyzed and compared with those of the Beryllium-VA group diatomic family species where data are available. The permanent dipole moments, transition dipole moments, Einstein emission coefficients, radiative lifetimes and Franck-Condon factors for interested Λ - S states are also derived. Further assessments of the spin-orbit coupling effect are performed for states associated with the first two dissociation asymptotes of BeSb. Four Λ - S states split into seven Ω states, and some of the PECs are distorted significantly through the spin-orbit coupling effect, which is similar to its isovalent diatomics BeAs. In consideration of potential risks of manipulating beryllium-containing species directly, the information associated with molecular structures, spectroscopic parameters as well as transition properties that provide in this paper is anticipated to serve as guidelines for further researches of BeSb.

Practical approach for beryllium atomic clusters: TD-DFT potential energy surfaces from equilibrium to dissociation for excited states of 2s → 2p

To shed light on the spectroscopic energy-smearing mechanism of the recently developed technique for multi-element analysis (e.g., forensic tests on artworks), which is called plume laser-induced fluorescence, practically computer simulations need to be accurate and fast enough for generating wide-range excited-state potential energy surfaces (PESs) from equilibrium to dissociation of large (non-equilibrated) atomic clusters. Currently, all the very high-level post-Hartree–Fock theories (e.g., coupled-cluster theory) are computationally too expensive for this purpose (e.g., taking at least ~ 23 years). After considering the extensive applications of time-dependent density-functional theory (TD-DFT) in computing the optical properties of many-body systems, we wonder how TD-DFT performs in the wide-range-PES generations because no such TD-DFT application is found by us in the literature (perhaps due to its insufficient static/non-dynamical correlation energy). In this work, we carried out TD-DFT calculations on beryllium atomic clusters from Be1 to Be50 (in contrast to open-shell H2 or Li2 system, we think the individual closed-shell Be systems at the dissociation limit could help TD-DFT to describe the static/non-dynamical correlation. For example, it is usually considered that Be2 has zero non-dynamical correlation energy in the literature) with and without Tamm–Dancoff approximation (TDA). Electronic excited-state properties (e.g., PES, equilibrium position, dissociation energy, fork intersection) associated with 2s → 2p are systematically investigated at a total of 48 levels of TD-DFT. Our calculations are thoroughly benchmarked against experimental results and (very) high-level theoretical values. In short, we find that for accurate simulations, it is necessary to use diffuse basis sets and the TDA approximation. TD-DFT with the small basis set 3-21+G* took ~ 2 min to finish a single-point excitation energy calculation on a linear Be50 (a toy model), while the large basis set 6-311+G(2df,2p) took 30 min. By contrast, a couple-cluster theory EOM-CCSD with 6-311+G(2df,2p) took 2.5 h to do the same but merely for a smaller linear Be10. In general, we suggest that TD-DFT:TDA with 3-21+G* should be practically fast and accurate enough for emulating our desired wide-range excited-state PESs of large Be atomic clusters (including conical intersection points of close energies) in the future studies. Nevertheless, benchmarking work on (much) larger sizes of Be clusters will always be more desirable whenever its computational costs at very high level of theories becomes more tractable.

Gravitational fragmentation and formation of giant protoplanets on orbits of tens of au

Aims. Migration of dense gaseous clumps that form in young protostellar disks via gravitational fragmentation is investigated to determine the likelihood of giant planet formation. Methods. High-resolution numerical hydrodynamics simulations in the thin-disk limit are employed to compute the formation and long-term evolution of a gravitationally unstable protostellar disk around a solar-mass star. Results. We show that gaseous clumps that form in the outer regions of the disk (>100 au) through disk fragmentation are often perturbed by other clumps or disk structures, such as spiral arms, and migrate toward the central star on timescales from a few thousand to few tens of thousands of years. The migration timescale is slowest when stellar motion in response to the disk gravity is considered. When approaching the star, the clumps first gain mass (up to several tens of MJup), but then quickly lose most of their diffuse envelopes through tidal torques. Part of the clump envelope can be accreted onto the central star causing an FU-Orionis-type accretion and luminosity outburst. The tidal mass loss helps the clumps to significantly slow down or even halt their inward migration at a distance of a few tens of au from the protostar. The resulting clumps are heavily truncated both in mass and size compared to their wider orbit counterparts, keeping only a dense and hot nucleus. During the inward migration, the temperature in the clump interiors may exceed the molecular hydrogen dissociation limit (2000 K) and the central region of the clump can collapse into a gas giant protoplanet. Moreover, migrating clumps may experience close encounters with other clumps, resulting in the ejection of the least massive (planetary-mass) clumps from the disk. We argue that FU-Orionis-type luminosity outbursts may be the end product of disk fragmentation and clump inward migration, preceding the formation of giant protoplanets on tens of au orbits in systems such as HR 8799.

Theoretical study of electronic properties and isotope effects in the UV absorption spectrum of disulfur

The electronic structures of triplet S2 ground and excited states are studied by ab initio molecular orbital and configuration interaction calculation. Potential energy curves correlated with S(3P)+S(3P) and S(3P)+S(1D) at the dissociation limit are evaluated, and electronic terms for a total of 11 states are assigned. Transition dipole moments, as a function of internuclear distance, are determined for two allowed transitions to B″3Πu and B3Σu- excited states. The total absorption cross-sections are computed to estimate isotope-fractionation constants, ε, for four most common isotopologues: 32S32S, 32S33S, 32S34S, and 32S36S by quantum close-coupling (R-matrix) expansion approach and they are found to lie in a mostly opaque to competing absorbers spectral window. We suggest that the photochemistry and isotopic effects of S2 are of significant importance and provide data showing high sensitivity of mass-independent fractionation to excitation wavelength. Zero-point energy based constants εZPE are estimated as well to compare with the obtained isotope effects and two modes for MIF are present in three-isotope plots; large isotopic effects were observed for both 36S and 33S with an excitation wavelength-dependent fluctuation.