New rotational line strengths for the C2 Swan system ( d Π g 3 – a Π u 3 ) have been calculated for vibrational bands with v ′ = 0 – 10 and v ″ = 0 – 9 , and J values up to J=34–96, using previous observations in 33 vibrational bands. Line positions from several sources were combined with the results from recent deperturbation studies of the v ′ = 4 and v ′ = 6 levels, and a weighted global least squares fit was performed. The updated molecular constants are reported. The line strengths are based on a recent ab initio calculation of the transition dipole moment function. A line list has been made available, including observed and calculated line positions, Einstein A coefficients and oscillator strengths (f-values). The line list will be useful for astronomers, combustion scientists and materials scientists who utilize C2 Swan spectra. Einstein A coefficients and f-values were also calculated for the vibrational bands of the Swan system.

Line strengths and updated molecular constants for the C2 Swan system

Potential curves for all 62 valence states of C2 have been computed using configuration interaction wavefunctions within the valence orbital space. The valence orbitals were determined by a multiconfiguration self‐consistent‐field calculation using a properly dissociating set of configurations for the a 3Πu state. Comparison is made with the experimental spectroscopic constants for ten of these states: Re values are too large by ∼0.05 ao, the bond energies De are too small by ∼0.8 eV, Te values are within ∼0.34 eV, and ωe is generally within ∼70 cm−1. We have identified 19 other possible bound states not yet observed experimentally, and have obtained a good qualitative picture of the positions and shapes of the repulsive states which may be involved in dissociation processes.

The valence states of C2: A configuration interaction study

New observations of the A1Πu-X1Σg+ transition (Phillips system) of C2

Rovibronic energy levels are determined for four low-lying electronic states (X  3 Σ - , A 3Π, a  1 Δ , and c  1 Π ) of the imidogen free radical ( 14 NH) using the M arvel (Measured Active Rotational-Vibrational Energy Levels) technique. Compilation of transitions from both laboratory measurements and solar spectra, found in 18 publications, yields a dataset of 3002 rovibronic transitions forming elements of a measured spectroscopic network (SN). At the end of the MARVEL procedure, the majority of the transitions form a single, self-consistent SN component of 2954 rovibronic transitions and 1058 energy levels, 542, 403, and 58 for the X  3 Σ - , A 3Π, and c  1 Π electronic states, respectively. The a  1 Δ electronic state is characterized by 55 Λ -doublet levels, counting each level only once. Electronic structure computations show that unusually the CCSD(T) method does not accurately predict the a  1 Δ excitation energy even at the complete basis set limit.

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MARVEL analysis of the measured high-resolution spectra of 14NH3

Ab initio configuration interaction calculations have been performed on the X 2Σ+, A 2Π, and B′ 2Σ+ states of MgH. Numerical values for the potential curves have been obtained for 23 internuclear distances between 2.2 and 9.5 a0. Dipole and transition moment functions have also been calculated. Spectroscopic constants obtained from the calculated potential curves are found to be in good agreement with experimental data; the maximum errors in Re, De, Te, and ωe are 0.003 nm, 0.09 eV, 0.05 eV, and 38 cm−1, respectively. The calculated band absorption oscillator strength for the X–A transition of 0.161 is believed to have ±20% accuracy.

A.J. Sauval

Papers

Study of molecular lines in the solar photospheric spectrum