Knowledge Bank

Small internal rotor molecules possess a complex rotational spectrum due to the interaction of rotational and torsional degrees of freedom and to the existence of low-lying torsional excited states. At the Duke Microwave Laboratory, we have in recent years studied the rotational spectra of a variety of these species at frequencies up to 1 THz. We have also made corresponding advances in the analysis of the rotational spectra of small internal rotors, chiefly by extending the classical PAM and IAM techniques. In the last year, we have started work on the spectrum of dimethyl ether and a novel method of analysis in which van Vleck perturbation theory is used only when appropriate. We have also continued work on the spectrum of $HNO3\nu 9$ and of methanol and its isomers. For $HNO3\nu 9$, we have extended our experimental studies of the torsional splittings to include states in which the symmetric top approximation to the splittings is invalid. We have analyzed all existing laboratory data for $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH3OH$ up to $J=22$ on a supercomputer and have measured and assigned a large number of excited torsional state transitions in $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH3OH$. In this talk, some of our recent progress will be discussed.