Jérôme Lozeille

Further investigations of the Ã←X̃ transition of the Kr·NO and Xe·NO complexes using (1+1) REMPI spectroscopy

Abstract The A←X transitions of the Kr·NO and Xe·NO molecular complexes have been recorded with improved quality. In both cases the origin band consists of a single feature, consistent with a (near) linear A state. The spectra demonstrate a wealth of structure, which increases in complexity to higher energy; this is interpreted in terms of a weakening of the interaction as the internal energy increases. Dissociation energies for both the X and A states are derived. Attempts to record the corresponding spectra for Ne·NO were unsuccessful. The trend in the binding energies in the X and A states of Rg·NO (Rg=He–Xe) is discussed.

High-quality interatomic potential for Li+·He

Abstract CCSD(T)/aug-cc-pVQZ and CCSD(T)/aug-cc-pV5Z methods have been employed to obtain accurate interatomic potentials for Li + ·He, from which spectroscopic parameters are derived. A potential is presented using the larger basis set consisting of 91 points ( R ⩾1.3 A). An accurate value for the long-range D 4 parameter could be obtained from the potential, but it was not possible to extract higher D n terms. Since accurate values for D n ( n =4, 6, 7 and 8) could be derived from literature data, these parameters were fixed (and damped), allowing the short-range potential to be fitted accurately to a Born–Mayer potential.

The à 2Σ+ state of Ar⋅NO

The  2Σ+ state of Ar⋅NO is studied using (1+1) resonance-enhanced multiphoton ionization (REMPI) spectroscopy. Higher quality spectra than obtained in other studies allow the identification of a number of previously unreported features. The spectrum is analyzed using two models: a rigid van der Waals complex in which NO is weakly bonded to Ar; and a complex in which the free internal rotation of NO is hindered by the anisotropy caused by the presence of the Ar atom. It is concluded that as the intermolecular stretch is excited, then the anisotropy decreases, and the angular motion of the complex becomes more and more like that of a free rotor. Near the origin, the complex has an average geometry approaching linear, whereas when the intermolecular stretch is excited, an average geometry closer to T-shaped occurs; however, when the anisotropy is small, the concept of geometry becomes ill-defined.

The Ã←X̃(1+1)REMPI spectrum and high-level ab initio calculations of the complex between NO and N2

The results of two separate studies of the complex between NO and N2 are reported. The (1+1) REMPI spectrum of the A←X transition of the complex between NO and N2 is presented of improved quality over that reported previously, and the appearance of the spectrum is discussed. The results of high-level ab initio calculations [RCCSD(T)/aug-cc-pVQZ//QCISD/6-311+G(2d)] on the X 2Π state are also reported. The indications are that the NO moiety is more freely rotating in the complex than is N2, and that a wide angular space is sampled in the zero-point energy level. The appearance of the REMPI spectrum suggests that the A 2Σ+ state is (close to) linear, and RCCSD(T)//QCISD calculations on the A state, using Rydberg-function-augmented basis sets, suggest that the lowest energy linear isomer is the ON⋅N2 linear orientation. It is clear, however, that the understanding of this complex, and its spectroscopy, is far from complete, and will be challenging.

Calculations on the unstable CO−(X2Π) anion

It is demonstrated that CO-(X(2)Pi) lies above CO(X(1)Sigma (+)) and hence is unstable with respect to autodetachment. This is in disagreement with an oft-cited experimental result, which concluded that CO has an electron affinity of +1.4 eV, but in agreement with electron scattering results. It might be concluded that the RCCSD(T) approach with aug-cc-pVQZ and aug-cc-pV5Z basis sets gives reliable electron affinities based upon comparison with identical calculations on N-2; however, analysis of the electronic wave function indicates that this may be fortuitous. On the other hand, CASSCF + multireference configuration interaction (MRCI) calculations on CO- seem to indicate a viable way forward, and spectroscopic constants are derived.