The effects of collisional quenching on photofragment emission (PFE) detection of vapor-phase HgCl(2) in combustion flue gas constituents are investigated. Exciting HgCl(2) via the 1(1)Pi(u)<--1(1)Sigma(g)+ transition, time-resolved measurements of emission from the Hg(6(3)P(1)) daughter in buffer-gas mixtures of N(2), O(2), and CO(2) indicate that the fragmentation pathway passes through a long-lived intermediate species, which we assign to Hg(6(3)P(2)). Total quenching rate coefficients of Hg(6(3)P(1)) by N(2), O(2), and CO(2) are consistent with values reported in the literature. In addition, total quenching rate coefficients for the intermediate Hg(6(3)P(2)) state are determined to be 1.72(+/-0.08)x10(-10) cm(3) molecule(-1) s(-1) and 2.90(+/-0.37)x10(-10) cm(3) molecule(-1) s(-1) for N(2) and O(2), respectively. An analysis of the impact of the collisionally dependent energy-transfer process that precedes the formation of Hg(6(3)P(1)) on the use of PFE to measure HgCl(2) concentration is presented.