Broadband ultraviolet absorption spectroscopy of the weak Cl-2 continuum between 250 and 400 nm was used to measure the molecular Cl-2 density in pure chlorine inductively coupled plasmas at pressures of 15-100 mTorr and radio-frequency (rf) power up to 800 W. The depletion of the Cl-2 density was greatest at high-rf power and low pressure, and reached 80% at 15 mTorr 800 W. A simple global model was developed to explain the variation of the Cl-2 dissociation rate as a function of source power and total gas pressure, and was in excellent agreement with the observations.