J.M. Robbe

Theoretical study of the perturbation parameters in the a3Π and A1Π states of CO

Completely ab initio calculations of the perturbation parameters of the a 3Π and A 1Π states of CO have been carried out and compared with the recent experimental results of Field et al. Use has been made of a new program for calculating off‐diagonal matrix elements of the B L · S and spin‐orbit coupling operators. By including configuration interaction functions built from Hartree‐Fock orbitals optimized for each state, good agreement has been obtained between calculated and experimental constants in most cases. Our results show that the perturbations have a strong dependence on R and that they are different for different pairs of states. The single configuration approximation gives a relative error up to 40% and the constancy of perturbation values found by Field et al. cannot be attributed to dependence on a single, constant parameter.

Predissociation mechanism for the lowest Πu1 states of N2

Separate coupled-channel Schrodinger-equation (CSE) models of the interacting Πu1 (b,c,o) and Πu3 (C,C′) states of N2 are combined, through the inclusion of spin-orbit interactions, to produce a five-channel CSE model of the N2 predissociation. Comparison of the model calculations with an experimental database, consisting principally of detailed new measurements of the vibrational and isotopic dependence of the Πu1 linewidths and lifetimes, provides convincing evidence that the predissociation of the lowest Πu1 levels in N2 is primarily an indirect process, involving spin-orbit coupling between the bΠu1- and CΠu3-state levels, the latter levels themselves heavily predissociated electrostatically by the C′Πu3 continuum. The well-known large width of the b(v=3) level in N214 is caused by an accidental degeneracy with C(v=9). This CSE model provides the first quantitative explanation of the predissociation mechanism for the dipole-accessible Πu1 states of N2, and is thus likely to prove useful in the constru...

A model of the B 1Σ+–D ’ 1Σ+ Rydberg–valence predissociating interaction in the CO molecule

The strong interaction between the B 3sσ 1Σ+ Rydberg state and the D’ 1Σ+ valence state of the CO molecule is shown to cause large changes in the vibrational and rotational constants of the B state, as well as predissociation of all rotational levels of B (v’=2) and a breaking off in the emission of B (v’=1) levels at J=36 in 12C 16O and J=37 in 13C 16O. A two‐state diabatic model of the Rydberg–valence interaction is constructed and vibrational term values, widths, and intensities are calculated by close coupling in order to account for the strong mixing. The model separates the differences between the spectroscopic constants of the B state and those of the ground state molecular ion into two components, one due to the R‐dependent quantum defect of the B state and another due to the strong Rydberg–valence perturbation. The perturbation is characterized by a constant coupling matrix element of 2900 cm−1 inside the crossing point of the two diabatic potentials, decaying to zero at long internuclear distanc...

Oscillator strengths, radiative lifetimes, and photodissociation cross-sections for CN

Abstract Self-consistent field (SCF) + configuration interaction (CI) wavefunctions were used to compute potential energy curves of all 2Σ+ and 2Π states lying in the range 0–13.6 eV. Transition moments have been determined between the ground state X2Σ+ and all excited 2Σ+ and 2Π states. Absorption oscillator strengths fv′v″ for the red and the violet systems are compared to experimental and theoretical determinations, and predicted fv′v″ values for the B2Σ+-A2Πi transition are given. Radiative lifetimes for the A2Πi and B2Σ+ states are also determined. From the calculated photodissociation cross-sections, a value of the photodissociation probability of CN in the interstellar medium equal to 10−9 sec−1 has been calculated.

Optical emission spectrum of the NO2+ dication

Abstract We recorded and rotationally analyzed a new emission band at 2563 A obtained from a low-pressure, hot cathode and magnetically confined electric discharge through pure NO vapor. The available experimental data from photoion-fluorescence photon coincidence and translational energy loss spectroscopy, in conjunction with ab initio calculation, allowed assignment of the new band to the B 2 Σ + - X 2 Σ + (0, 0) transition of the NO 2+ ion.

New electronic transitions in the N2+ ion: Rotational analysis of the D′2Πgr-A2Πui transition: Comparison of experimental and ab initio calculated molecular constants

Abstract Rotational analysis has been carried out for the first time for bands of the D ′ 2 Π g - A 2 Π u system of the N 2 + ion. At the same time, ab initio calculations were performed using the SCF method followed by full-valence configuration interaction calculations. Theoretical results are presented as required for interpretation of the spectra.

The first valence states of the SO+ ion: Rotational analysis of the A2Πi-X2Πr and b4Σ−-a4Πi transitions. Comparison of experimental and ab initio calculated molecular parameters

Abstract Rotational analysis has been carried out for the first time for bands of the A 2 Π i - X 2 Π r system of the SO + ion, as well as for newly discovered bands of the b 4 Σ − - a 4 Π transition of the same ion. At the same time, ab initio calculations were performed using the SCF method followed by configuration interaction. Theoretical results are presented as required for interpretation of the spectra. Important spin-orbit interactions are shown to occur between the four X 2 Π r , A 2 Π i , a 4 Π i , and b 4 Σ − states and neighboring unobserved states.

Electronic structure and perturbations: Interpretation in the SiO valence states

Abstract Using SCF-CI wavefunctions, we have calculated energies and spectroscopic constants of low-lying states of SiO. Special attention has been paid to the 3 Π states and has led to the prediction of a new state lying close to the observed c 3 Π i state. Ab initio calculations of parameters characteristic of the perturbations occurring between the valence states of SiO have been performed and compared to experimental deperturbation analysis of Field, Lagerqvist, and Renhorn.

Theoretical electronic structure and perturbations in SiS

Wavefunctions, SCF-CI energies, and spectroscopic constants of low-lying electronic states of SiS have been computed. Ab initio calculations of parameters characteristic of the perturbations occurring between the valence states of SiS have been performed. The results present, as in SiO, a large difference between 3Π and 1Π perturbation parameters. Predictions of the magnitude of the corresponding perturbations in heavier molecules (SiSe, SiTe) are reported.

Nonexponential decay of CS a 3Π–X 1Σ+ luminescence

The VUV photodissociation of CS2 embedded in argon or krypton matrices at 5 K yields to the formation of the CS a 3Π radical. A nonexponential decay of the CS (a→X) emission is observed which can be decomposed into three components. The radiative lifetimes of the 3Π0 and 3Π1 sublevels are calculated. The agreement between experimental and a b i n i t i o values leads to the conclusion that the three spin–orbit sublevels of the CS triplet state decay independently in low temperature matrices.