Carbon monoxide triplet Rydberg series in the f complex region

Using a multistep state-selective excitation scheme, fluorescence-dip spectra of carbon monoxide have been recorded in the energy region between 106 100 and 112 200 cm⁻¹. Prominent groups of bands were tentatively identified as transitions into the 6 f.10 f (v = 0) and 9pσ.11pσ (v = 0) triplet Rydberg series. For the f complex states, molecular constants have been calculated. The triplet f levels show an unusually large rotational constant and are located at higher energies than their singlet counterparts.