COUPLED-STATE ANALYSIS OF ROTATIONAL TRANSITIONS OF THE $GT$, $GG$, and $GG'$ CONFORMERS OF $N$-PROPANOL

Author Institution: Institute of Physics, Polish Academy of Sciences, Al. Lotnikow; 32/46, 02-668 Warszawa, Poland; Department of Physics, The Ohio State University, Columbus,; OH 43210The rotational spectrum of the most stable $Gt$ conformer of $n$-propanol has already been studied in some detail.}, 428 (2006).} Rotational transitions in the $Gg$ and $Gg'$ conformers of $n$-propanol, which are related to $Gt$ by rotation of the OH group, have also been assigned.} \vspace{0.2cm} Nevertheless, the single state analysis of the $Gt$ conformer and the two-state analysis of the $Gg$-$Gg'$ pair revealed various discrepancies, that suggested significant coupling between all three states. Attempts at a three-state $Gt$-$Gg$-$Gg'$ fit were unsuccessful until a level crossing type perturbation between $Gt$ and $Gg$ energy levels was identified in the $FASSST$ spectrum. This allowed a satisfactory three state solution to be located, and it became possible to account to within experimental accuracy for well over 6000 lines in the measured rotational spectrum. The resulting accurate relative energies of the pertinent conformers provide a benchmark for accurate $ab initio$ calculations, and are compared with results of a recent detailed computational study.}, 487-495 (2005).