MRCI Methods Research Articles

Study on photodissociation spectra and decay pathways of gas-phase PdCl3– and PdCl2– anions by electrospray ionization mass spectrometry and MRCI calculation

We investigate photodissociation of the gas-phase palladium complex anions, Pd(II)Cl3- and Pd(I)Cl2-, both experimentally and theoretically. Visible photodissociation mass spectrometry reveals that the main dissociation channels differ for Pd(II)Cl3- and Pd(I)Cl2-; the former yields neutral chlorine atom (Pd(I)Cl2- + Cl) whereas the latter affords chloride anion (Pd(I)Cl + Cl-). Absorption spectrum and photodissociation channels are predicted using the MRCI method. The observed absorption spectrum and dissociation product for Pd(II)Cl3- agree with the MRCI calculation, whereas those for Pd(I)Cl2- do not, which suggests that some relaxation process such as internal conversion significantly contributes to the photodissociation of Pd(I)Cl2-.

Spin-orbit coupling in excited electronic states of AgH

Potential energy curves have been calculated for the low-lying electronic states of AgH, correlating to the 4d10 5s1 (2S), 4d10 5p1 (2Po), 4d9 5s2 (2D), and 4d10 6s1 (2S) states of atomic silver, using the MRCI method with scalar relativistic and spin–orbit corrections. Spectroscopic constants were obtained for 24 individual Ω states, and several excited states of AgH observed in the ultraviolet absorption spectra, i.e., the C1Π, B1Σ+, b3Δ1, and D1Π states, were relabeled based on the new ab initio data. The calculated Einstein A coefficients indicated that almost all electronic transitions with ΔΩ = 0, ±1 are allowed.

Thermal rate constants and kinetic isotope effects of the H + H2O2 reactions: barrier height and reaction energy from single- and multireference methods.

One of the more significant sub-mechanisms of H2/O2 combustion involves the reaction of hydrogen peroxide with hydrogen atoms (H + H2O2), resulting in the production of OH + H2O (R1) and H2 + HO2 (R2) paths. Previous experimental and ab initio calculations reveal some variations in the barrier height for (R1). To improve the energetics of both (R1) and (R2), single reference and multireference ab initio methods are employed, and the rate constants and H/D kinetic isotope effects (KIEs) are calculated as a function of temperature. For (R1), the best results for the barrier height and reaction energies computed with the CASPT2(15,11)/aug-cc-pV6Z are 5.2 and - 70.3kcal.mol-1, respectively. CCSD(T)/aug-cc-pV5Z + CV (core-valence) calculations for (R2) give 9.7 and - 15.6kcal.mol-1 to those parameters. The CVT/SCT rate constants of both paths agree well with the fitted rate constants from uncertainty-weighted statistical analysis of the 14-mechanism of H2/O2. The kinetic isotopic effect (kH/kD) for the reaction D + H2O2 → DH + HO2 was found to be 0.47, which is in excellent agreement with the experimental value of 0.43. The structures of reactants, transition state, and products of (R1) and (R2) are calculated with the aug-cc-pVTZ basis set and M062X DFT, CCSD(T), and CASSCF methods. The barrier heights and reaction energies of (R1) and (R2) are computed using the M06-2X, CCSD(T), MRCI, and CASPT2 methods and various basis sets. The rate constants are calculated with the variational transition state theory including multidimensional tunneling corrections (VTST-MT), with potential energy surfaces built by the M06-2X/aug-cc-pVTZ approach.

Study of electronic structure and optical transition properties of low-lying excited states of AuB molecules based on configuration interaction method

High-level configuration interaction method including the spin-orbit coupling is used to investigate the low-lying excited electronic states of AuB that is not reported experimentally. The electronic structure in our work is preformed through the three steps stated below. First of all, Hartree-Fock method is performed to compute the singlet-configuration wavefunction as the initial guess. Next, we generate a multi-reference wavefunction by using the state-averaged complete active space self-consistent field (SACASSCF). Finally, the wavefunctions from CASSCF are utilized as reference, the exact energy point values are calculated by the explicitly correlated dynamic multi-reference configuration interaction method (MRCI). The Davidson correction (+Q) is put forward to solve the size-consistence problem caused by the MRCI method. To ensure the accuracy, the spin-orbit effect and correlation for inner shell electrons and valence shell electrons are considered in our calculation. The potential energy curves of 12 Λ-S electronic states are obtained. According to the explicit potential energy curves, we calculate the spectroscopic constants through solving radial Schrödinger equation numerically. We analyze the influence of electronic state configuration on the dipole moment by using the variation of dipole moment with nuclear distance. The spin-orbit matrix elements for parts of low-lying exciting states are computed, and the relation between spin-orbit coupling and predissociation is discussed. The predissociation is analyzed by using the obtained spin-orbit matrix elements of the 4 Λ-S states which spilt into 12 Ω states. It indicates that due to the absence of the intersections between the curves of spin-orbit matrix elements related with the 4 low-lying Λ-S states, the predissociation for these low-lying exciting states will not occur. Finally, the properties of optical transition between the ground Ω state <inline-formula><tex-math id="M3">\begin{document}$ {\rm A}^{1}{{{\Pi}}}_{1} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231347_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231347_M3.png"/></alternatives></inline-formula> and first excited Ω state <inline-formula><tex-math id="M4">\begin{document}$ {{\mathrm{X}}}^{1}{{{\Sigma }}}_{{0}^{+}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231347_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20231347_M4.png"/></alternatives></inline-formula> are discussed in laser-cooling filed by analyzing the Franck-Condon factors and radiative lifetime. And the transition dipole moment is also calculated. But our results reveal that the AuB is not an ideal candidate for laser-cooling. In conclusion, this work is helpful in deepening the understanding of AuB, especially the structures of electronic states, interaction between excited states, and optical transition properties. All the data presented in this paper are openly available at <ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.doi.org/10.57760/sciencedb.j00213.00009">https://www.doi.org/10.57760/sciencedb.j00213.00009</ext-link>.

Quantum chemical calculation of normal vibration frequencies of polyatomic molecules

Quantum calculation of molecular vibrational frequency is important in investigating infrared spectrum and Raman spectrum. In this work, a low computational cost method of calculating the quantum chemistry of vibrational frequencies for large molecules is proposed. Usually, the calculation of vibrational frequency of a molecule containing <i>N</i> atoms needs to deal with the Hessian matrix, which consists of second derivatives of the 3<i>N</i>-dimensional potential hypersurface, and then solve secular equations of the matrix to obtain normal vibration modes and the corresponding frequencies. Larger <i>N</i> implies higher computational cost. Therefore, for a limited computational hardware condition, higher-level computations for large <i>N</i> atomic molecule’s vibrational frequencies cannot be implemented in practice. Here we solve this problem by calculating the vibrational frequency for only one vibrational mode each time instead of calculating the Hessian matrix to obtain all vibrational frequencies. When only one vibrational mode is taken into consideration, the molecular potential hypersurface can be transformed into one-dimensional curve. Hence, we can calculate the curve with high-level computational method, then deduce the expression of one-dimensional curve by using harmonic oscillating approximation and obtain the vibrational frequency by using the expression to fit the curve. It should be noted that this method is applied to vibrational modes whose vibrational coordinates can be completely determined by equilibrium geometry and the molecular symmetry and be independent of the molecular force constants. It requires that there exists no other vibrational mode with the same symmetry but with different frequencies. The lower computational cost for a one-dimensional potential curve than that for 3<i>N</i>-dimensional potential hypersurface’s second derivatives permits us to use higher-level method and larger basis set for a given computational hardware condition to achieve more accurate results. In this paper we take the calculation of<i> B</i><sub>2</sub> vibrational frequency of water molecule for example to illustrate the feasibility of this method. Furthermore, we use this method to deal with the SF<sub>6</sub> molecule. It has 7 atoms and 70 electrons, hence there exists a large amount of electronic correlation energy to be calculated. The MRCI is an effective method to calculate the correlation energy. But by now no MRCI result of SF<sub>6</sub> vibrational frequencies has been reported. So here we use MRCI/6-311G* to calculate the potential curves of A<sub>1g</sub>, E<sub>g</sub>, T<sub>2g</sub> and T<sub>2u</sub> vibrational modes separately, deduce their expressions, then use the expressions to fit the curves, and finally obtain the vibrational frequencies. The results are then compared with those obtained by other theoretical methods including HF, MP2, CISD, CCSD(T) and B3LYP methods through using the same 6-311G* basis set. It is shown that the relative error to experimental result of the MRCI method is the least in the results from all these methods.

Ab initio study of palladium dichloride PdCl2 and its anion PdCl2−

We theoretically study geometries and electronic structures of palladium dichloride PdCl 2 and its anion PdCl 2 − , using the MP2 (or CASPT2) and MRCI methods. Spin singlet and triplet PdCl 2 and doublet PdCl 2 − are investigated. As a result of geometry optimization, both linear and bent geometries are obtained for singlet and triplet PdCl 2 and only linear geometries for doublet PdCl 2 − ; it is found that there are two minima (linear and bent) on the ground 1 1 A 1 state for singlet PdCl 2 and the bent minimum is energetically lowest in neutral PdCl 2 . It is of great importance to note that the total energies of all calculated states for linear PdCl 2 − are predicted much lower in energy than the ground 1 1 A 1 state for linear singlet PdCl 2 , indicating that the PdCl 2 − anion is electronically stable. The equilibrium electron affinity of bent 1 1 A 1 PdCl 2 is calculated 4.61 (4.10) eV with the MRCI (MRCI + Q) method.

Theoretical spin-orbit calculations of low-lying electronic states of cerium monoxide

The 69 Ω lowest lying electronic states of CeO molecules have been investigated by employing MRCI and CASPT2 ab initio methods and by including the Spin Orbit Coupling (SOC). The potential energy curves (PECs) of all the lowest singlet and triplet Λ−S states below 22,850 cm−1 have been constructed and considered to calculate the related spectroscopic properties. The obtained results of Λ-S states and their corresponding Ω components have been successfully compared to the available experimental parameters. Based on these results, the component 3Φ2 (Ω=2) of the ground state X3Φ has been assigned as the lowest substate of CeO. 23 unobserved components have been predicted for the first time and new assignments have been given for many observed states. Dipole-allowed transition moments between the predicted electronic states have been reported. Vibrational levels up to v = 5 for the first seven lowest components (1)(Ω=2), (1) (Ω=3), (1) (Ω=1), (2)(Ω=2) (1)(Ω=0−), (2)(Ω=1) and (1)(Ω=0+) have been obtained by solving the radial Schrodinger equation to study the possible perturbations between these levels.

Ab initio MRCI study on potential energy surfaces for double Cl loss from the palladium tetrachloride anion PdCl42−

We theoretically study double Cl loss from the palladium tetrachloride anion PdCl42− using the ab initio MRCI method. The double Cl loss is probably a significant process in the laser-induced particle formation of Pd in aqueous/EtOH solution which was proposed recently by Saeki et al. (M. Saeki et al., J. Phys. Chem. C 123 (2019) 817). It is predicted that the wave packet created on excited potential energy surfaces (PESs) by the UV irradiation at 266 nm temporally propagates on the PESs and finally spreads over a flat region, where neutral Cl and anionic Cl− are generated.

Conformers of dehydrogenated glycine isomers.

We report a comprehensive ab initio investigation of the conformers of dehydrogenated glycine radicals using the STO-3G, 3-21G, and aug-cc-pVDZ (aVDZ) basis sets and the UHF and UMP2 (H2 N-CH-COOH and HN-CH2 -COOH) as well as MCSCF and MRCI (H2 N-CH2 -COO) methods via two different conformational search strategies generating initial structures for optimizations by (a) removing H atoms from glycine conformers and (b) scanning torsional angles describing internal rotation along the CC, CN, and CO (except for H2 N-CH2 -COO) bonds of the radicals. We find four H2 N-CH-COOH {InCH , IInCH , IIInCH , IVnCH } and seven HN-CH2 -COOH {IpNH , IIpNH , IIInNH , IVpNH VnNH , VIpNH , VIIpNH } conformers with classical(adiabatic) relative energies of {0.00(0.00), 1.57(1.55), 5.25(5.03), 9.85(9.72)} and {0.00(0.00), 0.78(1.06), 1.93(2.08), 3.34(3.16), 3.39(3.29), 5.00(4.86), 9.27(8.87)} kcal/mol, respectively, obtained with UCCSD(T)-F12b/aug-cc-pVTZ(+UCCSD(T)-F12b/aVDZ ZPE correction) and four H2 N-CH2 -COO {IpCOO , IInCOO , IIIpCOO , IVnCOO } conformers with MRCI-F12+Q/aVDZ(+MRCI/aVDZ ZPE correction) energies of {0.00(0.00), 1.65(1.64), 1.78(1.75), 2.21(2.21)} kcal/mol, where n and p denote C1 and Cs symmetry. The MRCI-F12+Q[UCCSD(T)-F12b] InCH → IpNH and InCH → IpCOO classical(adiabatic) isomerization energies are 18.51(17.32)[21.20(20.01)] and 31.88(31.66) kcal/mol, respectively.

Ab initio MRCI study on potential energy curves for a single Cl loss from the palladium tetrachloride anion PdCl42−

We theoretically investigate a single Cl loss from the PdCl42− anion, which is a candidate for key processes in the laser-induced particle formation of Pd in aqueous/EtOH solution proposed recently by Saeki et al. (M. Saeki et al., J. Phys. Chem. C 123 (2019) 817). We calculate low-lying potential energy curves (PECs) of PdCl42− as a function of a Pd-Cl bond length with the MRCI method. It is found that PdCl42− is excited to a 1Eu state by UV irradiation, followed by a Pd-Cl bond elongation on the repulsive 21A1 and/or 21B1 PECs, leading adiabatically to the Cl− formation.

Ab initio calculations on low‐lying electronic states of PdH

AbstractPotential energy curves for the low‐lying electronic states of PdH have been calculated using the MRCI method with scalar relativistic and spin‐orbit corrections, and all electronic states correlating to the 4d10 (1S), 4d9 5s1 (3D), 4d9 5s1 (1D) and 4d8 5s2 (3F) states of Pd were included. Potential energy curves for the individual Ω states have been obtained, and the experimentally observed spectra of both PdH and PdD isotopologues have been assigned appropriately based on the ab initio results. Einstein A coefficients were calculated for other possible transitions from the low‐lying electronic states to the X2Σ+ ground state. Diagonal and off‐diagonal matrix elements of the spin‐orbit Hamiltonian were calculated for all vibrational levels of the X2Σ+, 12Δ, 12Π, 22Σ+ and 32Σ+ states, and it was found from the eigenvectors that the vibrational wavefunctions of the 12Δ3/2 and 12Π3/2 states are mixed significantly in both PdH and PdD isotopologues.

A new potential energy surface of the LiHO+ system and the dynamics studies of the O + LiH+ reaction

A potential energy surface (PES) for the lowest 2A′ state of LiHO+ is constructed using ab initio calculations. The MRCI method with AVQZ and AV5Z basis sets is employed during the calculations. The artificial neural network is utilized to fit the analytical PES based on 28,552 energy points which are extrapolated to the complete basis set limit. The reaction dynamics of the O + LiH+ ⟶ Li+ + HO reaction is investigated by means of quasi-classical trajectory method. The dynamics results show that the reaction mechanism dominating the title reaction changes from indirect to direct mechanism with increasing collision energy.

Accurate spectroscopic constants of the lowest three electronic states in halonitrenes with multireference configuration interaction

AbstractInternally contracted multireference configuration interaction (icMRCI) calculations of the ground state (X3Σ−), the first excited state (a1Δ) as well as the second excited state (b1Σ+) have been performed for a series of halogenated nitrenes NXs (X = Cl, Br, and I). Accurate spectroscopic constants of these lowest three electronic states of each NX were obtained in this work using MRCI methods with aug‐cc‐pVXZ (X = T, Q, 5) basis sets and complete basis set (CBS) limit. In addition, various corrections, including the Davidson correction, scalar relativistic effect, core‐valence correlation, and spin‐orbit coupling effect, have been studied in calculating spectroscopic constants, especially for heavy‐atom nitrenes. Comparisons have been made with previous computational and experimental results where available. The icMRCI + Q calculations presented in this work provide a comprehensive series of results at a consistent high level of theory for all of the halogenated nitrenes.

Rovibrational spectrum calculations of four electronic states in carbon monoxide molecule: Comparison of two effect correction methods

Accurate calculation of molecular energy is of great significance for studying molecular spectral properties. In this work, the potential energy curve and rovibrational spectrum (Gν) of the ground state X1∑+ and the excited states a3Π, a'3∑+ and A1Π of carbon monoxide molecule are calculated by the multi-reference configuration interaction method. In the calculation, the core-valence correlation correction (CV) effect and scalar relativistic (SR) effect are included.In order to obtain an accurate energy of molecule, two computational schemes are adopted. In the first scheme, i.e. (m MRCI+Q/CBS(TQ5)+CV+SR), the molecular orbital wavefunction is obtained from the Hartree-Fock self-consistent field method by using the basis set aug-cc-pVnZ. The wavefunction is first calculated by the state-averaged complete active space self-consistent field approach. Then the multi-reference configuration interaction method (MRCI) is adopted to calculate the dynamic correlation energy in the potential energy curve. Finally, we use the basis set cc-pCVQZ and aug-cc-pVQZ to calculate the CV effect and SR effect by the MRCI method. In the second scheme (aug-cc-pwCVnZ-DK (n=T, Q, 5)), the potential energy curves (PECs) of these four electronic states are calculated by the MRCI method whose basis set (aug-cc-pwCVnZ-DK) contains the CV effect and SR effect. Finally, in order to reduce the error caused by the basis set, we extrapolate the basis sets of the two computational schemes to the complete basis set. On the basis of the PECs plotted by the different methods, we obtain the spectroscopic parameters of the X1∑+, a3Π, a'3∑+ and A1Π states of the carbon monoxide by solving the internuclear Schrödinger equations through utilizing the numerical integration program “LEVEL”.In this paper, we calculate the SR effect and the CV effect by using different schemes, and the latter is indispensable for accurately calculating the molecular structure. For the lowest two electronic states, we consider the dependence of the two effects on the calculation of the Gaussian basis group (Method B), and find that the accuracy of the rovibrational spectrum is improved. It can be seen that these electronic states have higher requirements for electronic correlation calculation. For higher electronic states, the electron cloud distribution is relatively loose, and the electronic correlation obtained by a single Gaussian basis group can achieve the corresponding calculation accuracy. Of course, since the calculation of the rovibrational spectra is essentially only the relative energy, the offset effect of the electronic correlation effect of different electronic states is also included here in this paper.

Electronic structure of the polar molecules XF (X: Be, Mg, Ca) with rovibrational and dipole moment calculations

A theoretical investigation for the feasibility of laser-cooling is performed through the calculation of accurate potential energy curves, static dipole moments, spectroscopic constants and rovibrational calculations for 24, 26 and 27 highly excited electronic states for BeF, CaF and MgF molecules respectively. In order to understand the electronic structure of their lowest lying electronic states and to learn the characteristic behavior of their chemical bonding, a high level of calculation is realized by using the complete active space self-consistent field (CASSCF) with multi-reference configuration interaction MRCI method including single and double excitations with Davidson correction (+Q) for the three considered molecules. The comparison between the values of the present work and those available in the literature for several electronic states shows a good agreement. Fifty new excited electronic states have been investigated, in the present work, for the first time for the three studied molecules.

Calculations on rovibrational spectra of two lowest electronic states in sulfur monoxide molecule by explicitly correlated approach

Accurate spectroscopic constants and rovibrational level information are of great importance in molecular physics and astrophysical field. In this work, a new computational scheme is presented to further improve the accuracy of spectroscopic constants, and the two lowest electronic states of sulfur monoxide molecule are investigated as a typical case study. High-level ab initio calculations are carried out to compute the potential energy curves (PECs) of the lowest bound states, the ground triplet states X3Σg-, and the first excited singlet states a1Δg of SO molecule. The explicitly correlated multi-reference configuration interaction method (MRCI-F12) and cc-pCVQZ-F12 basis set are adopted in the electronic structure computations. The Davidson correction is taken into account to eliminate the size-consistency error. The core-valence (CV) electron correlations of the n=2 shell of S atom and n=1 shell of O atom are estimated by the MRCI-F12 method, whereas only the 1 s orbital of S atom is excluded in the CV calculations. Moreover, we introduce the scalar relativistic effect into our study by utilizing the second-order Douglas-Kroll and Hess (DKH) one-electron integrals by the MRCI method through combining with the uncontracted cc-pCVQZ-F12 basis set. On the basis of the PECs of the SO dimer, the spectroscopic constants (Te, Re, ωe, ωeχe, Be, αe and De) of the two electronic states are determined by solving the one-dimensional nuclear rovibrational Schrödinger equations. Our spectroscopic constants are found to be in excellent agreement with previous experimental and theoretical values. Furthermore, the detailed information about the vibrational energy levels and rotation spectroscopic constants (Bν, Dν) of the two states is also presented with a deviation of 0.1% order of magnitude from the available experimental results. Our present computational work is valuable for future experimental studies on the rovibrational energy levels for the SO molecule and also indicates that the MRCI-F12 approach is cheap and accurate and expected to have wide applications in the PECs of other small molecular systems.

An ab initio investigation on the ground electronic state of chlorine monoxide and its singly charged cation and anion

The MRCI method has been utilized to calculate the equilibrium structure of the ground electronic state for the ClO radical and its singly charged cation and anion, ClO+ and ClO−. The augmented correlation-consistent basis sets up through sextuple-zeta quality are used to derive equilibrium structural parameters, potential energy curves and spectroscopic constants of the systems. Two extrapolating schemes enable us to remove the basis set truncation error and to estimate the complete basis set limit. Corrections of core-valence correlation and relativistic effect are included in our calculations. By solving the radial Schrödinger equation of nuclear motion, the vibrational energy levels as well as rotational and centrifugal distortion constants of the ground electronic states for the three species are obtained. Ionization potentials and the electron affinities are also obtained on the RCCSD(T)/AV6Z level. The knowledge extracted from this work are anticipated to extend our understanding on molecular characteristics of the ClOn (n=−1, 0, +1) systems and can serve as guidelines for further experimental or theoretical researches.

Multi-reference Ab initio calculations of 3d transition-metal dimers: Sc2

The problem of calculation of the electronic structure of transition-metal clusters (even dimers) still presents a challenge for computational chemistry. The reason is that the expansion of the ground state wave function on electronic configurations does not contain a principal configuration and a large number of reference configurations must be treated equally. Thus, the multi-reference (MR) approaches are, in general, mandatory. A short description of the MRCI methods is presented. The calculation of Sc2 at the MRCISD(+Q)/cc-pV5Z level, showed that the its ground state corresponds to a quintet, 5Σu−, in agreement with experiment and previous precise calculations. The triplet 3Σu− state is located about 1.1 kcal/mol above. We calculated the ground state, X5Σu−, of the Sc2 dimer by the MRCISD(+Q) method at the complete basis set (CBS) limit. This is the first MRCISD(+Q) calculation of 3d transition-metal clusters at the CBS limit. From the Mulliken population analysis and comparison with atomic energies follows that in the ground state Sc2 dissociates on one Sc in the ground state and the other in the second excited quartet state, 4Fu. The spectroscopic parameters of the ground potential curve, obtained by the Dunham analysis at the valence MRCISD(+Q)/CBS level, are: Re = 5.20 bohr, De = 50.37 kcal/mol, and e = 234.5 cm−1. The obtained value for the harmonic frequency agrees very well with the experimental one, e = 239.9 cm−1. From the indistinguishability of identical atoms in quantum mechanics follows that in spite of an asymmetric dissociation limit for Sc2, both Sc atoms have the same electron population and it is incorrect to consider them as different. Therefore, the accepted classification of the dimer states should be revised, since some of them are forbidden by the Pauli Exclusion Principle.

Ab initio study of ground and low-lying excited states of MgLi and MgLi+ molecules with valence full configuration interaction and MRCI method

The ground and low-lying excited states of MgLi and MgLi+ molecules have been investigated. The potential energy curves and the permanent and transition dipole moments of the MgLi and MgLi+ molecules are determined making use of the multi-reference configuration interaction and valence full configuration interaction with large basis sets. The core–valence correlation and scalar relativistic correction are also taken into account with aug-cc-pCVQZ basis set and the third-order Douglas–Kroll Hamiltonian approximation, respectively. The transition dipole moments are used to evaluate the radiative lifetimes of the vibrational levels for the low-lying excited states of the MgLi and MgLi+ molecules. The derived spectroscopic constants of the ground and low-lying excited states are in good agreement with available experimental and theoretical works.

Effect of 5-methylresorcinol on spin conversion in molecular oxygen

Geometric parameters of 5-methylresorcinol (MR) molecules in different spin states (1,3,5MR) and its complexes with oxygen (1,3(O2-MR)) are determined within the DFT/B3LYP method. Cross-sections of potential energy surfaces of the formation reaction of the intermolecular complex 1,3(O2-MR) are plotted in MCSCF functions by the MRCI method. With regard to the spin-orbit interaction the moments of spin-allowed and spin-forbidden transitions of the complexes are calculated and the possibility of spin conversion in 3O2 under the effect of MR is analyzed.