Millimeter-wave spectrum of n-PrCHO. (a) Zoomed view of the millimeter-wave spectrum that shows the dominant quadruple degenerated lines of the cis-gauche conformer, which contains pairs of a- and b-type R-branch transitions. The final predicted spectrum of this conformer, computed for 300 K, is given for comparison (a-type lines are depicted in red, and b-type lines are depicted in green). (b) Zoomed-in view of the millimeter-wave spectrum that shows unblended quadruplets of a- and b-type R-branch transitions of the cis-trans conformer with K_a = 0,1 at J″ = 41 (left panel) and J″ = 42 (right panel). Intensity is given in arbitrary units.