Reading between the lines: Exposing underlying features of high resolution infrared spectra (CHC1F₂)

A technique to facilitate the assignment of congested high resolution IR spectra is presented. It involves subtraction of component spectra simulated from known spectroscopic constants. Application to the v₂ (1313.1 cm^-1) and v₇ (1351.7 cm^-1) bands of CHC1F₂ led to rovibrational line assignments for less intense and overlapping features including the minor isotopomer CH³⁷C1F₂ and c-type lines of CH³⁵C1F₂. The number of transitions assigned to the fundamental bands increased from 1721 to 6031 for ³⁷Cl, and from 7496 to 9664 for ³⁵Cl, with a greater range of rotational quantum numbers than found in a previous study. A total number of 1457, 484 and 262 line assignments were made for 2₀ ¹9₁₁, 7₀ ¹9₁ ¹ and 2₀ ¹6₁ ¹ hotbands respectively, features otherwise completely obscured in the observed spectrum. Rotational and centrifugal distortion parameters were fitted for all the upper states.