The microwave spectrum of CO in the a 3Π state. II. The submillimeter wave transitions in the normal isotope

Abstract

Precise measurements of the frequencies of a number of new rotational transitions of a 3Π CO (v=0–4) in the range 250–500 GHz are reported. In addition earlier measurements of the J=0–1 frequencies near 90 GHz have been repeated at higher precision and extended to include the v=6 lines. The nonlinear least-squares analysis of this microwave data combined with the lambda doublet transition frequencies of Klemperer and co-workers was carried out for v=0–4 by direct diagonalization of a Hamiltonian matrix that included the relevant v subblock of the a 3Π state along with the subblocks for v′=0–10 of the a′ 3Σ+ state. The new frequencies make possible the determination from the rf-microwave data set of several parameters that previously had to be assumed, and the method of treating most of the a–a′ perturbations directly in the large matrix yields parameters, especially lambda doubling constants, which vary less, but more smoothly, with J than before. The later smoothness is found to be enhanced by inclusion of an off-diagonal, spin–spin interaction in the a–a′ perturbation Hamiltonian, as was done in published fits of FTIR spectra of the a′ 3Σ+–a 3Π system. We also discuss the theory of the perturbed Zeeman effect of a 3Π CO, along with some preliminary measurements, and report a value of the pressure broadening parameter for a typical rotational transition in this state.