On the Separation of the Broadening-Relaxation Time and Molecular Concentration from Pure-Rotational Spectroscopic Intensity Data

The broadening-relaxation time τ and the molecular concentration N of the absorbing species become separable at the transition frequency if a new intensity coefficient Γ is substituted for the conventional Beer's Law intensity coefficient γ. This investigation reveals that Γ generally can be factored into two measurable terms, η and φ. η is shown to be linear with molecular concentration and independent of relaxation time and φ is a dimensionless function of the broadening-relaxation time. The essence of this separation is that it is possible to fix to a constant value the number of radiation excited transitions each molecule will undergo during the molecular rotational relaxation time. When the number of transitions per molecule is the same for all relaxation times, the amount of radiation absorbed during the relaxation time is proportional to the molecular concentration of the absorbing species. The theory has been subjected to experimental examination. Several of the results are presented and discussed. This intensity coefficient gives rise to a new line shape, which is compared with the conventional line shape.