Qunchao Fan

The alkaline earth dimer cations (Be2 +, Mg2 +, Ca2 +, Sr2 +, and Ba2 +). Coupled cluster and full configuration interaction studies†

Although all of the neutral alkaline earth dimers have been studied experimentally, only for the beryllium and strontium systems have the diatomic radical cations been subjected to modern spectroscopic techniques. In the present research, both coupled cluster and full configuration interaction methods were used to describe the M2 + systems. Basis sets as large as aug-cc-pCV5Z were chosen. For both Be2 + and Sr2 + agreement with the experiments is outstanding. Final predictions for the unknown dissociation energies are 10,651 (Mg2 +), 9605 (Ca2 +), and 8980 cm−1 (Ba2 +). The M2 + dissociation energies decrease monotonically going down the periodic except for the Sr2 + - Ba2 + pair. The unknown bond distances re are 3.015 (Mg2 +), 3.814 (Ca2 +), 4.194 (Sr2 +), and 4.587 Å (Ba2 +).

Studies on the P-branch spectral lines of rovibrational transitions of diatomic system.

An analytical formula is used to predict the accurate P-branch spectral lines of rovibrational transitions for diatomic systems. The formula is derived from elementary expression of molecular total energy by taking multiple spectral differences. It is not only reproduces the known experimental transition lines by using a group of fifteen known experimental transition data, but also predicts the accurate spectral lines that may not be available experimentally. The P-branch emission spectra of the (0,1), (0,2) and (0,3) bands of the B(2)∑(+)→X(2)∑(+) system in the (12)C(17)O(+) molecular ion are studied, and correct values of the unknown spectral lines up to J=80.5 for each band are predicted using the formula.

A variational algebraic method used to study the full vibrational spectra and dissociation energies of some specific diatomic systems

The algebraic method (AM) proposed by Sun et al. is improved to be a variational AM (VAM) to offset the possible experimental errors and to adapt to the individual energy expansion nature of different molecular systems. The VAM is used to study the full vibrational spectra {Eυ} and the dissociation energies De of (4)HeH(+)-X(1)Σ(+), (7)Li2-1(3)Δg,Na2-C(1)Πu,NaK-7(1)Π, Cs2-B(1)Πu and (79)Br2-β1g((3)P2) diatomic electronic states. The results not only precisely reproduce all known experimental vibrational energies, but also predict correct dissociation energies and all unknown high-lying levels that may not be given by the original AM or other numerical methods or experimental methods. The analyses and the skill suggested here might be useful for other numerical simulations and theoretical fittings using known data that may carry inevitable errors.

A new type of sandwich compound: homoleptic bis(trimethylenemethane) complexes of the first row transition metals

The metal carbonyl complexes [η4-(CH2)3C]Fe(CO)3 and [η4-(CH2)3C]Cr(CO)4 have been synthesized containing the umbrella-shaped trimethylenemethane ligand. The prospect of using this ligand in the metal sandwich complexes [(CH2)3C]2M (M = Ti, V, Cr, Mn, Fe, Co, Ni) has now been investigated by density functional theory. The lowest energy structures of such complexes have the metal atom sandwiched between two tetrahapto trimethylenemethane ligands. Singlet spin state structures are strongly preferred for the titanium and nickel derivatives and doublet spin state structures for the vanadium and cobalt derivatives. Similarly, the triplet spin state is preferred for the iron derivative by more than 11 kcal mol−1. The preferred spin states for the chromium and manganese derivatives depend on the functional used for the structure optimization. Thus the B3LYP and B3LYP* methods predict the higher spin states, namely triplet for chromium and quartet for manganese. However, the BP86 method predicts the lower spin states of singlet for chromium and doublet for manganese. The higher spin state structures for the late transition metal derivatives, namely quintet [(CH2)3C]2Fe, quartet [(CH2)3C]2Co, and triplet [(CH2)3C]2Ni, have trihapto rather than tetrahapto trimethylenemethane ligands. The frontier molecular orbitals in the singlet [(CH2)3C]2M derivatives (M = Ti, Ni) suggest strong metal–ligand σ and π bonding but insignificant metal–ligand δ bonding.

New Potential Energy Surface Features for the Li + HF → LiF + H Reaction

The existing potential energy surfaces for the Li + HF system have been challenged by the experiments of Loesch, Stienkemeier, and co-workers. Here a very accurate potential energy surface has been obtained with rather rigorous theoretical methods. Methods up to full CCSDT have been pursued with basis sets as large as core correlated quintuple ζ. Reported here are the reactants, products, two transition states, and three intermediate complexes for this reaction. These reveal one previously undiscovered equilibrium geometry. The stationary point relative energies are very sensitive to level of theory. The reaction has a classical endothermicity of 2.6 kcal mol(-1). The complex Li···HF in the entrance valley lies 6.1 kcal/mol below the reactants. The expected transition state Li···H···F is bent with an angle of 72.2° and lies 4.5 kcal/mol above the reactants. The latter predicted classical barrier should be no more than one kcal/mol above the exact barrier. Not one but two product complexes lie 1.6 and 2.2 kcal/mol above reactants, respectively. Between the two product complexes, a second transition state, very broad, is found. The vibrational frequencies and zero-point vibrational energies (ZPVE) of all stationary points are reported, and significantly affect the relative energies.

Studies on the full vibrational energies and dissociation energies of some heteronuclear diatomic molecules

A parameter-free analytical formula for dissociation energies of diatomic molecules is proposed by Fan and Sun (2009) [20] based on LeRoy and Bernsteins vibrational energy expression near dissociation limit. Using three highest vibrational energies which may be generated by the algebraic method (AM) presented in our previous study and by some other physical methods, the new formula is applied to study the molecular dissociation energies of 10 electronic states of KH, (7)LiD, (7)LiH, (6)LiH, NaK, NaLI and NaRb heteronuclear diatomic molecules which have regular (Morse-like) potentials in this work. The results show that the AM energies E(upsilon)(AM) and dissociation energies D(e)(AM) have excellent agreement with experimental values.

Theoretical study of LiCl− and LiBr− molecular ions

The molecular structures and spectroscopic constants of the ground electronic states of LiCl− and LiBr− are investigated with the coupled-cluster method. To improve the accuracy of our calculations, we have employed the extrapolation schemes as well as corrections of the core–valence correlation and scalar relativistic effect. The equilibrium parameters, potential energy curves, force constants, vibrational energy levels and spectroscopic parameters of both molecular ions are derived, in which those of LiBr− are reported for the first time. The electron affinities and vertical detachment energies of neutral and anionic LiCl and LiBr are also evaluated.

Modeling intermediates in carbon monoxide coupling reactions using cyclooctatetraene thorium derivatives

The interaction of carbon monoxide with organoactinides has recently been shown experimentally, particularly by Cloke and co-workers, to result in coupling to give the oligomeric anions CnOn2− (n = 2, 3, 4). In order to model possible intermediates in reactions of this type, we have used density functional theory to explore the systems (C8H8)Th(CO)n (n = 1 to 5) and (C8H8)2Th2(CO)n (n = 2 to 7) related to the known “thorocene”, (η8-C8H8)2Th. Thorium was chosen as the actinide for this work since its chemistry almost entirely involves the single diamagnetic +4 oxidation state. All of the binuclear (C8H8)2Th2(CO)n structures found in this work have long Th⋯Th distances ranging from 4.4 to 5.0 A suggesting the absence of direct Th–Th bonds. Two (C8H8)2Th2(CO)2 isomers of similar energies in which the two CO groups have coupled to form trans and cis isomers of a bridging η4-μ-C2O2 ligand are low energy structures. These bridging η4-μ-C2O2 ligands exhibit ultralow ν(CO) frequencies around 1000 cm−1 indicating strong back donation of thorium d and f electrons into C–O antibonding orbitals. Most of the carbonyl richer (C8H8)2Th2(CO)n (n = 3 to 7) structures are derived from one of these basic (C8H8)2Th2(CO)2 structures by addition of terminal CO groups. An exception is the lowest energy (C8H8)2Th2(CO)4 structure which has C4v symmetry with four equivalent separate η2-μ-CO groups bridging the thorium atoms. The thermochemistry of these systems suggest (C8H8)Th(CO)4 and (C8H8)2Th2(CO)n (n = 2, 4) to be the most promising synthetic objectives, which are potentially obtainable by reductive carbonylation of the known (C8H8)ThCl2.

Binuclear pentalene manganese carbonyl complexes: conventional trans and unconventional cis structures

The binuclear pentalene manganese carbonyl trans-(η5,η5-C8H6)Mn2(CO)6 has been synthesized by the reaction of the pentalene dianion with a manganese carbonyl halide. This species as well as its decarbonylation products (C8H6)Mn2(CO) n (n = 5, 4, 3) have been investigated by density functional theory. In all of these optimized structures both pentalene rings are bonded to manganese atoms as pentahapto ligands. The lowest energy (C8H6)Mn2(CO)6 structure is the experimentally observed singlet trans structure but a closely related cis structure lies ∼7 kcal/mol higher. The lowest energy (C8H6)Mn2(CO)5 structure is a singlet structure having a four-electron donor bridging CO group and a Mn–Mn single bond of length ∼2.9 Å. The lowest energy (C8H6)Mn2(CO)4 structure is a singlet structure having all terminal CO groups and a short Mn ≡ Mn triple bond of length ∼2.3 Å. For (C8H6)Mn2(CO)3 low energy structures are found with either triplet or quintet spin states. Low energy structures with pentalene rings only partially bonded to manganese atoms were found for the carbonyl-rich species (C8H6)Mn2(CO) n (n = 7, 8). However, the latter species are predicted not to be viable with respect to carbonyl loss to give the stable (C8H6)Mn2(CO)6.

Relativistic configuration interaction calculations on the Kα x-ray spectra of sulfur

The transition energies, transition rates and absorption oscillator strengths of Kα x-ray from S XV to S VIII have been calculated by multiconfiguration Dirac–Fock and relativistic configuration interaction calculation with the inclusion of Breit interaction, quantum electrodynamics and finite nuclear mass corrections in the extended optimal levels scheme. The transition rates have been calculated in Babushkin and length gauges. This work firstly reports the complete Kα x-ray spectra of sulfur, and the results were compared with the available calculative and experimental results on He-like and Li-like sulfur. The corresponding present results are in good agreement with them, and the rest of transitions for the study of the present results are new ones. These wide ranging data can provide useful parameters for the study of the sulfur plasma.