THE STRENGTHS, WIDTHS, AND SHAPES OF INFRARED LINES: II. THE HCl FUNDAMENTAL

The methods described in Part I are applied in detail to the determination of strengths, widths, and shapes of the vibration–rotation lines of the 1–0 bands of HCl 35 and HCl 37 observed at 300°K. The variation of the line strengths with rotational quantum numbers is compared with theory to yield a value of the ratio of the permanent electric dipole moment to the product of the effective charge and the equilibrium internuclear distance of + 0.988 ± 0.022. The band strength was found to be 130 cm −2 atm −1 which should be good to ~ 5%. A marked variation of line width with rotational quantum number has been found which follows approximately the Boltzmann population distribution. This result is compared with a theory that considers resonant dipole–dipole and billiard ball interactions. The line widths were found to vary from ~ 0.25 cm −1 atm −1 for J = 3 to ~ 0.07 cm −1 atm −1 for J = 13. Evidence is obtained that at distances greater than ~ 1.5 cm −1 from the line centers the absorption is greater than is given by the Lorentz line shape. In the wings of the lines the absorption is better represented by a line shape varying as (ν –ν 0 ) −η where η ~ 1.8.