Knowledge Bank

The results of new analysis of the high resolution Fourier transform far infrared (FIR) absorption spectrum of the torsion rotational band of $CH3$ OD will be presented. Based on a recently determined set of molecular constants for $CH3ODa$ we have been able to assign 1126 assigned Fourier transform far- infrared (FIR) transitions that involve the second excited torsional levels with $\nu t=2.ACH3$ OD data set that contains 460 microwave (MW), millimeter wave (MMW) transitions and 3474 Fourier transform FIR transitions with $vt\le 2$ and $J\le 21$ has been fit using a reduced torsion-rotational Hamiltonian obtained from the one-large-amplitude internal rotation model. The MW and MMW transitions have been fit with a root-mean-square (rms) deviation of 0.12 MHz while FIR transitions have rms deviation of $0.00026cm-1$ using 61 parameters. These deviations are on the order of the experimental uncertainties, indicating that the MW, MMW and FIR spectral transitions have been fit to the desired accuracy and the reduced torsion-rotational Hamiltonian model is capable of accurately describing $CH3OD$ energy levels up through the second excited torsional level. The success of the fit demonstrates that the increased general asymmetry in $CH3OD$, compared to $CH3OH$, can be accounted for adequately by the reduced Hamiltonian model.