INTENSITY MEASUREMENTS IN B3PI0+U-X1SIGMA0+G SYSTEM OF I2

Equivalent width measurements were made on rotational lines in six vibrational bands in the B-X system of I2. All measurements were made photoelectrically. Calculations of the Doppler, natural, and collisional widths show the Doppler width to be 340 times larger than the combined natural and collisional width at 22°C. Measurement of the equivalent width at several path lengths for each line confirmed a pure Doppler curve of growth for the lines. From known spectroscopic data the line strengths gave a value for the square of the electronic contribution to the transition moment, and for the value of the total Einstein spontaneous emission rate from each v′ to all v″ with nonzero Franck-Condon factors. A comparison of these purely radiative decay rates with total decay rates measured by Chutjian, Link, and Brewer and by Davis and Grimes shows the presence of a significant amount of spontaneous predissociation of the B state to ground-state 2P 3/2 iodine atoms. In the absence of collisions approximately 66% of the molecules which enter the B state predissociate, while only 34% radiate to the X state. In the presence of collisions, at 0.238-torr I2 pressure, approximately 20% spontaneously predissociate, 10% radiate to the X state, and 70% leave the B state by a process or processes which are nonradiative and collision dependent. Measurements were also carried out on the 25-0 band in the presence of a 15-kG magnetic field. No change in the equivalent width was observed in the presence of the field, indicating that the coupling to the repulsive state causing magnetically induced predissociation is insufficient to change the f value of the rotational transition.