Using an ab initio methodology, we compute the potential energy curves and the spinorbit coupling integrals of the N 2 electronic states located in the 0-120000 cm -1 energy domaine.In our analysis, we focus mostly on those located outside the Franck-Condon regio n accessible from the ground state of N 2 i.e. the two strongly bound states 1 3 Σ g -and 1 1 Γ g , and the weakly bound state 2 3 Σ g -, in addition to several repulsive states. We characterize them spectroscopically and we compute their spin-orbit couplings to the close lying singlets, triplets and quintets. This work completes our knowledge on the electronic states of N 2 that may be important intermediates during N + N collisions and for the dynamics of the N 2 singlets and triplets and quintets VUV photodissociation.

The branching ratios for the N(4 S) + N(2 D), N(4 S) + N(2 P), and N(2 D) + N(2 D) channels are measured for the photodissociation of X v J N ; 0, g 2 1 () S  =  + in the vacuum ultraviolet (VUV) region of 100,808-122,159 cm −1 using theVUV-VUV pump-probe approach combined with velocity-map-imaging-photoion detection. No evidence of forming the ground-state N(4 S) + N(4 S) products is found. No potential barrier is observed for the N (2 D) + N(2 D) channel, but the N(4 S) + N(2 P) channel has a small potential barrier of ≈740 cm −1. The branching ratios are found to depend on the symmetry of predissociative N 2 states instead of the total VUV excitation energy, indicating that N 2 photodissociation is nonstatistical. When the branching ratios for N(4 S) + N(2 D) and N(4 S) + N (2 P) products are plotted as a function of the VUV excitation energy for the valence N 2 1 Π u and 1 u S + states, oscillations in these ratios are observed demonstrating how these channels are competing with each other. These data can be used to select both the velocity and internal states of the atomic products by picking the quantum state that is excited. High-level ab initio potential energy curves of the excited N 2 states are calculated to provide insight into the mechanisms for the observed branching ratios. The calculations predict that the formation of both N(4 S) + N(2 D) and N(4 S) + N(2 P) channels involves potential energy barriers, in agreement with experimental observations. A discussion of the application of the present results to astronomy, planetary sciences, and comets is given.

Large calculations are done to investigate the valence and inner-valence electronic states of aluminum monochloride and its cationic species AlCl+ and AlCl2+, allowing their definite assignment. This concerns particularly the computations of the potential-energy curves of the electronic states of these species and their spin-orbit couplings and transition moments. An accurate set of spectroscopic constants for these species is also deduced. For the neutral molecule, our calculations show that the lifetimes of the AlCl A1pi v' > or = 10 levels are reduced to the 0.1-0.01 ps time scale because of spin-orbit induced predissociation processes and by tunneling through the potential barrier of the A state. Our potential curves for the ground state of AlCl and those of the cationic and dicationic species are also used for predicting the single and double ionization spectrum of AlCl. For both the cation and the dication, long-lived rovibrational levels are predicted.

The photoinduced ring-closure/ring-opening reactions of a series of bis-dithienylethene derivatives, as free ligands and Zn(II)-complexes, are investigated by resorting to theoretical (time-dependent density functional theory) and kinetic analyses in solution. The originality of the system stems from the tunability of the photoreaction quantum yields and conversion yields as a function of the electronic structure. The latter could be varied by modifying the electron-donating character of the DTE-end substituents L(a-d) (o,o) (a, D = H; b, D = OMe; c, D = NMe(2); d, D = NBu(2)) and/or the Lewis character of the metal ion center L(a-d)ZnX(2) (o,o) (L(a-c), X = OAc; L(d), X = Cl). The orbital description of the doubly-open form (o,o) and half-closed form (o,c) predicts that double closure to the form (c,c) would occur using UV irradiation. Photokinetic studies on the complete series demonstrate that photocyclization proceeds following a sequential ring closure mechanism. They clearly point out distinct quantum yields for the first and second ring closures, the latter being characterized by a significantly lower value. Dramatic decrease in both the quantum yields of the ring-closure and ring-opening processes is demonstrated for the complex L(d)ZnCl(2) exhibiting the strongest charge-transfer character in the series investigated. These studies show that this series of DTE derivatives provides an efficient strategy to tune the photochromic properties through the combination of the electron-donor and electron-acceptor (D-A) groups.

We use large scale ab initio calculations to investigate the valence and valence-Rydberg quintet states of N(2), their transition moments and their spin-orbit couplings to the close lying triplet electronic states. In addition to the A' (5)Sigma(g)(+) and the C" (5)Pi(ui) states already known, we identify two weakly bound states (2 (5)Sigma(g)(+) and 2 (5)Pi(u)) at approximately 95,300 and 106,200 cm(-1) above N(2)(X (1)Sigma(g)(+), v=0). The other quintets are viewed to be repulsive in nature. Our potentials and couplings are used later to derive a set of accurate spectroscopic data for these quintets, their spin-orbit constants, and to elucidate the quintet-triplet dynamics and the role of these newly identified quintets for the production of cold atomic nitrogen.

Accurate ab initio calculations are performed at the aug-cc-pV6Z/MRCI level of theory on the potential energy curves of SH (A2Σ+, 4Σ−, 2Σ−, 4Π) and SH+ (A3Π, 5Σ−), and on their respective mutual spin–orbit coupling integrals. These data are incorporated into Fermi golden rule computations allowing deducing the predissociation lifetimes for SH A2Σ+ and SH+ A3Π rovibrational levels and their corresponding deuterated species. An excellent agreement is found between the experimentally known values and ours, allowing reliable lifetime predictions for the upper A state rovibrational levels not measured yet.

UV-visible absorption spectroscopy and harmonic light scattering measurements coupled with density functional theory (DFT) calculations have been carried out for a series of 4,4'-bis(X-styryl)-2,2'-bipyridine M(II) dichloride complexes (M = Co, Ni, Cu, Zn; X = H, OMe, SMe, NMe(2), NEt(2), CN, NO(2)). The roles of the metal and the substituent X on their coordination geometries, absorption, and quadratic nonlinear optical properties have been investigated. We show that these complexes all exhibit a high-spin configuration and display a distorted tetrahedral metallic environment except the copper ones, which are distorted square-planar complexes. When X is a strong electron-donating group (X = NMe(2), NEt(2)), TDDFT calculations clearly demonstrate that, whereas the Zn complexes show an ILCT transition in the visible range, the Co, Ni, and Cu complexes exhibit additional MLCT and LLCT transitions. These latter transitions are vectorially opposed to the ILCT and could contribute to the decrease of the experimental quadratic hyperpolarizability beta values, in the order Zn > Ni approximately Cu > Co. The computation of the beta values using TDDFT for the whole series of the closed-shell Zn(II) complexes featuring different X substituents established that the NLO activity increases with the donating strength of X and more generally with the decrease of the HOMO-LUMO energy gap. When X is a strong withdrawing group, the drastic decrease of the NLO response is explained by the negligible participation of the HOMO-LUMO transitions.

Highly correlated ab initio calculations are employed for the structural and spectroscopic characterization of small odd chains of type C 2n+1 H, considering neutral forms, cations, and giving special attention to the anions. This work confirms the stability of the linear carbon chains and carbon clusters containing three-body rings. The smallest species, C 3 H, displays three stable structures, whereas C 5 H possesses at least 8 neutral isomers and 11 and 10 isomers with a negative or a positive charge. The equilibrium geometries, which can be candidates for laboratory and astrophysical detection, are studied using the RCCSD(T)-F12 and MRCI/CASSCF levels of theory, specifying properties for various electronic states. Four different stable isomers are confirmed for the C 5 H − anion. They are two rings and two chains, all showing singlet ground electronic states. The viability of the triplet linear form of C 5 H − (¥ C v (X 3 Σ −)) postulated in previous works, is not confirmed because it appears to be really dependent on the electron correlation energy denoting instability. A quasi-linear singlet (C s (X 1 A′)) represents a secondary minimum. Electronic state crossing occurs close to the linear structure where spin-orbit effects are negligible. The most stable structure of C 5 H − is a three-carbon cycle in which rotational constants have been determined to be A 0 =35479.86 MHz, B 0 =3618.29 MHz, and C 0 =3280.10 MHz. Its dipole moment is relatively large (6.4086 D).