Table 2. Physical properties of the anions used in this study.

	HS–	HSe–	Cl–	Br–
Ionic radius (Å)33	1.70 a	1.84 b	1.67	1.82
pKa (conj. Acid, H2O)18,40	7.0	3.7	–8.0	–9.0

^aIonic radius of S^2–.

^bIonic radius of Se^2–.