Microwave and millimeter wave study of Ortho-N2 states of CO–N2

Abstract

Microwave and millimeter wave transitions of the CO–N2 complex were investigated using three different instruments, namely, a pulsed molecular beam Fourier transform microwave spectrometer in the frequency region from 4 to 26 GHz, a microwave-millimeter wave double resonance spectrometer in the frequency regions from 8 to 18 GHz for the microwave and 107–118 GHz for the millimeter wave range, and an OROTRON spectrometer in the frequency range from 107 to 132 GHz. Both a- and b-type transitions associated with the ground-state K=0 levels and the lower K=1 levels of the ortho-N2 states, and with rotational quantum number J up to 19, were measured and analyzed. Nuclear quadrupole hyperfine splittings due to the presence of two equivalent N14 nuclei were resolved and analyzed to give additional information about the angular anisotropy of the interaction potential. The nuclear quadrupole coupling constants obtained are χaa=0.196 41(52) MHz for K=0 levels, and χaa=−1.0391(17) MHz, χbb=0.0633(17) MHz for the lower K=1 levels, respectively. The drastic difference between these two sets of coupling constants suggests that the orientation and motion of the N2 subunit are very different in these two states, and that the complex cannot be adequately described by a semirigid rotor model. In addition, measurements of the rotational spectra of the two new isotopomers containing C13O16 and C13O18 subunits provide further important information about the CO–N2 interaction potential.