Infrared emission spectrum and potential constants of HCl

The emission spectrum from a low-pressure hydrogen chloride flame has been recorded in the 3.1-5.3 μm region at high resolution using a 4.5-m grating spectrometer coupled to a PDP-15 computer. The data obtained for the v → v - 1 band sequence, with v = 1 to 6 for H³⁵Cl and v = 1 to 5 for H³⁷Cl, were combined with other accurate data and analyzed to obtain the vibrational and rotational constants and Dunham coefficients for the H³⁵Cl and H³⁷Cl molecules. Using this information, eighth-order nonlinear least-squares estimates of the Dunham, Simons-Parr-Finlan, Ogilvie, and Sandeman potential constants were computed. While the values of all four sets of constants display a lack of convergence, the constants of Sandeman's expansion exhibit better statistical behavior than the other three. This suggests that a Sandeman-like inversion of the Simons-Parr-Finlan and Ogilvie potential constants would be worthwhile.