Quintet electronic states of N2.

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.

Ionospheric chemistry: Theoretical treatment of ONOO(+) and of NO3(+).

In light of accurate ab initio calculations, we discuss the charge transfer, vibrational and electronic de-excitations between O(2)/O(2)(+) + NO(+)/NO and O/O(+) + NO(2)(+)/NO(2) through the formation and decomposition of NO(3)(+) and ONOO(+). For that purpose, we generated the potentials of the electronic ground and excited states of the colliding and molecular species involved in these reactions. We used configuration interaction methods and a large basis set. We predict multistep pathways, which involve both the long range and the molecular regions of the potential energy surfaces of the electronic states of the stable isomers of NO(3)(+) and those of the weakly bound charge transfer complex ONOO(+). The couplings between these electronic states such as vibronic, Renner-Teller, Jahn-Teller, and spin orbit are believed to play crucial roles during these important ionospheric ion-molecule reactions.

Sign reversal of the spin-orbit constant for the C 3Pi(u) state of N2.

Ab initio calculations are performed at the multireference configuration-interaction level of theory on the diagonal spin-orbit functions for the lowest non-Rydberg states of (3)Pi(u) symmetry in molecular nitrogen. Spin-orbit constants deduced from the ab initio results confirm the recent suggestion, based on new experimental results, that the C (3)Pi(u) state of N(2), long known to be regular in the region of its potential-energy curve minimum, becomes inverted at higher energies. By removing the effects of the crossing C(') (3)Pi(u) state, it is shown that A(v) for the C state changes sign from positive to negative near v=8, corresponding to a change in principal molecular-orbital configuration from (1sigma(g))(2)(1sigma(u))(2)(2sigma(g))(2)(2sigma(u))(3sigma(g))(2)(1pi(u))(4)(1pi(g)) to (1sigma(g))(2)(1sigma(u))(2)(2sigma(g))(2)(2sigma(u))(2)(3sigma(g))(1pi(u))(3)(1pi(g))(2) at an internuclear distance near 1.4 A.

OOCO+ cation I: characterization of its isomers and lowest electronic states.

Accurate ab initio calculations are performed in order to investigate the stable isomers of OOCO+ and its electronic states at both the molecular and asymptotic regions. These calculations are done using large basis sets and configuration interaction methods. Our theoretical computations predict the presence of four stable forms: A global minimum where a weakly bound charge transfer complex (OOOC+) may be found. Few tenths of cm(-1) above in energy, the OOCO+ very weakly bound isomer is predicted. At 1.75 eV above OOCO+, a strongly bound centrosymmetric isomer (c-CO3+) is located. For energies >8 eV, a third isomer of C(2v) symmetry is found where one oxygen is in the center. The one-dimensional potential energy surface cuts of these electronic states reveal the existence of shallow potential wells for OOCO+ and OOOC+ and of deep potential wells for the two other forms, where electronically excited molecules can be formed at least transiently. Finally, the electronic states of each isomer should interact by spin-orbit, vibronic, Renner-Teller, and Jahn-Teller couplings in competition with isomerization processes converting one form to another.

OOCO+ cation. II. Its role during the atmospheric ion-molecule reactions.

For the charge transfer and vibrational and electronic deexcitations between O2/O2+ + CO+/CO, O/O+ + CO2+/CO2, and C/C+ + O3+/O3, multistep reaction pathways are discussed in light of the theoretical data of this and previous paper together with close comparison with the experimental observations. Our calculations show that these pathways involve both the long range and molecular region ranges of the potential energy surfaces of the electronic states of the stable isomers of OOCO+ and mostly those of the weakly bound charge transfer complex OOCO+. The couplings between these electronic states such as vibronic, Renner-Teller, Jahn-Teller, and spin orbit are viewed to play crucial roles here. Moreover, the initial orientation of the reactants, in the entrance channels, strongly influences the reaction mechanisms undertaken. We propose for the first time a mechanism for the widely experimentally studied spin-forbidden exothermic O+((4)S(u))+CO2(X (1)Sigmag+)-->O2+(X (2)Pi(g))+CO(X (1)Sigma+) reaction where the O turns around the OCO molecule.

Ab initio investigations of the C3+ cation and of its role during the reactions of C3+ ions against atomic sulfur.

Accurate ab initio calculations are performed in order to characterize the most stable isomers of empirical formula C3S+ and the role of C3S+ during the ion-molecule reactions between the C3+ triatomic molecular ions and S atoms. The linear form l-C C-C-S+ (X2sigma+) is found to be the most stable isomer followed by a three-membered carbon ring with an external S {c-C3S+ (X2A1)}. The ion-molecule reactions are investigated by doing suitable 1-D cuts of the 6-D potential energy functions (PEFs) of the lowest electronic states of C3S+. After its formation, the C3S+ intermediate may dissociate leading, in addition to the charge transfer products, to C, C+, C2, C2+, CS, CS+, C2S and C2S+ species. Generally, the dynamics of these reactions are found to involve several electronic states of C3S+ and their mutual couplings, including Renner-Teller couplings, spin-orbit interactions and vibronic interactions. These couplings can take place before and/or after intramolecular isomerisation processes.