Results are reported for experimental measurements of the room-temperature chemical reactions between ground-state Hg center dot+ ions and 16 important environmental and biological gases: SF6, CO, CO2, N2O, D2O, CH4, CH3F, O-2, CH3Cl, OCS, CS2, NH3, C6F6, NO2, NO center dot, and C6H6. The inductively coupled plasma/selected-ion flow tube tandem mass spectrometer used for these measurements has provided both rate and equilibrium constants. Efficient electron transfer (> 19%) is observed with CS2, NH3, C6F6, NO2, NO center dot, and C6H6, molecular addition occurs with D2O, CH4, CH3F, CH3Cl, and OCS, and SF6, CO, CO2, N2O, and O-2 showed no measurable reactivity with Hg center dot+. Theory is used to explore the stabilities and structures of both the observed and unobserved molecular adducts of Hg center dot+, and reasonable agreement is obtained with experimental observations, given the uncertainties of the theory and experiments. A correlation is reported between the Hg center dot+ and proton affinities of the ligands investigated. Solvation of Hg center dot+ with formic acid was observed to increase the rate of electron transfer from NO center dot by more than 20%.