Publication costs assisted by the U. S. Atomic Energy CommissionThe absolute quenching cross sections for Hg(3P1) with a number of quenching gases have been obtained in a steady-state photolytic experiment. The intensity of 2537-8, emission has been followed as a function of absorbed intensity, and also pressure of the quenching gas. Low Hg concentrations are maintained in order to avoid the complication of radiation imprisonment. Quenching rate constants are determined from modified Stern-Volmer plots. The results are compared to cross sections from Zemansky type experiments on a relative basis and in several cases to the absolute results of Yarwood, Strausz, and Gunning who applied Holstein theory to Zemansky type experimental results. Comparison is also made to other low opacity studies and, where possible, to the relative cross sections determined from chemical methods. Generally, good agreement is obtained. NO provides the only gross disagreement in these comparisons of the nine molecules studied. IntroductionThe quenching of the 3P1 state of mercury by a foreign gas represents probably the most extensively investigated and most useful primary photochemical system. The fundamental photophysical processes in this system are indicated in the following mechanism