FORBIDDEN TRANSITIONS IN DIATOMIC MOLECULES: IV. THE a′3Σ+ ← XlΣ+ AND e3Σ− ← X1Σ+ ABSORPTION BANDS OF CARBON MONOXIDE

Abstract

Two examples of forbidden electronic transitions in heteronuclear molecules, 3Σ+ – 1Σ+ and 3Σ− – 1Σ+, are studied in the spectrum of the CO molecule. The bands have been obtained in absorption in the region 1750 to 1230 Å with absorbing paths up to 400 cm-atm., using the fourth and fifth orders of a 3 meter vacuum spectrograph. In most of the 3Σ+ – 1Σ+ bands all four predicted branches are observed. For the 3Σ− – 1Σ+ bands, a somewhat unusual structure is predicted: two branches of O and S form and three branches of Q form. In the best-resolved bands, four branches are observed which closely fit the predicted branches, two of the Q branches being very nearly coincident and unresolved in the present spectra. The rotational and vibrational constants of the upper states, a′3Σ+ and e3Σ− of the two band systems have been determined. Some of these data had previously been obtained from perturbations in other band systems of CO. On the whole, the perturbation data agree satisfactorily with the more precise data obtained directly in the present study.