Fourier transform spectroscopy of CO intercombination bands

Abstract

Several bands of CO intercombination systems have been recorded for the first time under high-resolution Fourier transform spectroscopy: B 1Σ +- e 3Σ −(0−1), B 1Σ +- d 3Δ i (0−5), and B 1Σ +- d 3Δ i (0−12), B 1Σ +- a′ 3Σ +(0−14), and B 1Σ +- a′ 3Σ +(0−17). The emission spectrum was produced from an electric discharge through a mixture of formic acid and helium. Observed wavenumbers of rotational lines (0 < J < 19) are presented. The line position uncertainties range from 0.001 to 0.02 cm −1, depending on the transition intensity. These bands are forbidden by electric-dipole selection rules and borrow intensity from the main Angstrom B 1Σ +- A 1Π system, via spin-orbit interactions. It is shown that these data are consistent with recent studies of perturbations arising in the A 1Π levels. In addition, the mixing coefficients, which represent the fractional A 1Π character of each line, are also reported.