Reinvestigation of the vacuum ultraviolet spectrum of CO and isotopic species: The B1Σ + ↔ X1Σ + transition

Abstract

The vacuum ultraviolet band spectrum system B 1Σ +- X 1Σ + of 12C 16O, 13C 16O, 12C 18O, and 13C 18O has been extensively investigated both in absorption and in emission with the Meudon Observatory national 10-m vacuum spectrograph. A band lying at 109.9 nm in 12C 16O is observed for all isotopes but only in absorption. It is shown to be the B- X(2-0) band. Molecular parameters of the B( v = 0, 1, 2) levels have been derived from simultaneous least-squares fits of the absorption and emission data pertaining to each of these vibrational levels. In addition, a simultaneous fit of the data for the different isotopes provided mass independent Dunham coefficients and equilibrium constants for the B state. Our values obtained for ω e and ω e x e confirm the recent determinations which are in disagreement with the values tabulated in standard references. The emission bands exhibit sudden weakenings typical of predissociation. This predissociation further manifests itself in the v = 2 level by a conspicuous broadening of the absorption lines. It may also be the cause of the displacement and anomalous B values observed for this level. From the Dunham coefficients, the following molecular constants (in cm −1 except for r e ) for the B state have been derived: T e=86926.9 r 3=1.1197 A ̊ . ω e ω ex e B e α e 10 6D e 12C 16O 2161.7 5 39.8 4 1.961 3 0.026 2 6. 5 13C 16O 2113.5 6 38.0 8 1.874 9 0.024 5 6. 0 12C 18O 2109.5 3 37.9 3 1.867 7 0.024 4 5. 9 13C 18O 2060.1 2 36.1 8 1.781 2 0.022 7 5. 4 14C 16O 2071.5 2 36.5 8 1.801 0 0.023 1 5. 5