The emission spectra from a magnesium dc arc in hydrogen or deuterium have been photographed at high resolution from 600 to 850 nm. Thirteen new bands of MgH and 18 of MgD in the B′2Σ+–X2Σ+ system have been identified and complete rotational analyses have been performed. Term values have been obtained for all bound ground state rotational levels of MgH for ν = 4–9 and MgD for ν = 6–13 and limiting curves of dissociation have been used to determine the dissociation energy of MgH. The experimental value, D00″(MgH) = 1.27 ± 0.03 eV is in excellent agreement with theory. The ground state RKR potential curve and Franck–Condon factors for the B′–X system are reported. Data on the isotopic molecules 25MgH, 26MgH, 25MgD, and 26MgD have also been obtained.

The absorption spectrum of the Mg2 molecule, which occurs in a furnace containing Mg vapor, has been photographed with a high resolution spectrograph. The rotational structures of the bands have been analyzed and the rotational and vibrational constants of the two states determined. The bands are found to arise from a 1Σ–1Σ transition between a very lightly bonded ground state and a more stable excited state. The R.K.R. potential energy curve of the ground state, which has a dissociation energy of 399 cm−1, has been determined. The more important constants of the ground state are ωe = 51.12 cm−1, ωexe = 1.64 cm−1, re = 3.890 Å and those of the upper state are ωe = 190.61 cm−1, ωexe = 1.14 cm−1, re = 3.082 Å.

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We report the first gas phase spectroscopic study of iron monocarbide. FeC molecules were generated in a laser vaporization molecular beam source and detected by laser induced fluorescence. Twenty-six vibronic bands have been recorded in the 430–500 nm region. Rotational analyses have been carried out for 22 of the bands. There are three lower states involved, two with Ω″=2 and one with Ω″=3. Based on our experimental observations and the ab initio calculations on RuC [Shim et al. J. Phys. Chem. 91, 3171 (1987)] the observed bands are interpreted as 3Δi←3Δi and 1Δ←1Δ transitions. The ground state electronic configuration is assigned to 1δ39σ1. Evidence for three excited electronic states (one 3Δi state, one 1Δ state and another state with Ω′=3) and for perturbations in several of their vibrational levels is presented.

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