<i>l</i>-Type Doubling in C2H2 and HCN

Abstract

A high-resolution infrared grating spectrometer has been used to investigate l-type doubling of energy levels of the linear molecules C2H2 and HCN. Resolving power of 145 000 was obtained at 4100 cm—1 which permitted the resolution of the Q branch of ν1+ν51(Σg+→πu) of C2H2 to J″ = 6. The difference between the B′—B″ value determined from the Q branch and the same quantity obtained from the P and R branches of this band yields a value of q = 4.72×10—3 cm—1. The doublet structure in the difference band 0110→0112(π→π) of HCN has been resolved for J″≥6 in the R branch and J″≥10 in the P branch. This π→π band is treated as two bands with slightly different molecular constants. Evaluation of rotational constants shows that different α values are obtained for the + and — components of these π states. The difference in frequency between lines of equal J″ in the 000→002 and 0110→0112 bands is shown to be a quadratic function of J″. The value obtained for q′ was 7.68×10—3 cm—1.