Intensities

In the analysis and characterization of rotational spectra, it is usually expected that if spectral assignment and analysis of the frequencies has been successfully carried out that this establishes the values of the quantum mechanical angular momentum operators well enough that a DC Stark Effect measurement (to establish the components of the electric dipole moment) allows the calculation of rotational intensities. Most, if not all, astronomical analyses assume this. Indeed, our CES analyses are based on using the intensities of ground vibrational state lines as a reference. This both avoids the need to accurately measure pressures and provides a useful benchmark for our intensity calibration. In our work on semi-rigid molecules the residuals of the intensity fit to were 1-2%. When this procedure was used for methanol, a number of residuals in excess of 40% were observed. Since the QM intensities are not consistent with the experimental intensities, it was necessary to select a subset for use in for the measurement of $T$ and $nL/Q$. Figure: Methanol Intensity Percentage Difference shows the percentage differences for all of the original 326 reference lines, but from a fit that excluded the lines whose intensities were outerliers.