Infra-red chemiluminescence II. Spectroscopic data

The technique described in part I has been used to obtain constants of interest in molecular spectroscopy. The vibration-rotation interaction factor, F for HCl has been evaluated from the infra-red emission spectrum. The critical parameter in F is θ = M0/M1re, where M0 and M1 are the first two coefficients in the electric dipole moment expansion about the equilibrium internuclear distance re. A value of θ = + 1.12 ± 0.18 has been obtained. It is shown that for molecules with θ = +1 the total band intensity in emission is independent of the rotational distribution in the vibrational state from which the emission occurs. This has been made use of in evaluating radiative transition probabilities. For the HCl v(3-1) transition a value for |R31|2 (= 1.60 x 10-4 debye2) was obtained for the first time. The same method yields a value of |R21|2/ |R20|2 = 204, in good agreement with an earlier estimate from absorption data.