achiral, 20 aci-nitro compounds, 20 acid, 21 acid anhydrides, 21 acid deposition in atmospheric chemistry , 22 acid rain in atmospheric chemistry , 22 acid-labile sulfur, 22 acidity, 22 acidity constant, 23 acidity function, 23 acidosis, 23 acid–base indicator, 23 actinic, 24 actinic flux , 24 actinism, 25 actinometer, 25 action spectrum, 25 activated adsorption process, 25 activated carbon, 26activated charcoal, 26 activated complex, 26 activation, 26 activation analysis (nuclear), 27 activation cross-section, 27 activation energy (Arrhenius activation energy), 27 activation in electrochemical corrosion , 28 activation in radiochemistry , 28 activation reaction, 28 activator, 28 active centre, 29 active medium, 29 active metal in electrochemical corrosion , 29 active site in heterogeneous catalysis , 29 active solid, 30 active species, 30 active state in electrochemical corrosion , 30 active transport in biology , 30 activity, 30 activity, of a radioactive material , 31 activity coefficient, , , 31 activity (relative activity), , 32 acute toxicity, 32 acyl carbenes, 32 acyl groups, 32 acyl halides, 33 acyl shift (1,2-, 1,3-, photochemical), 33 acyl species, 33 acylals, 34 acyloins, 35 acyloxyl radicals, 35 addend, 35 addition, 35 addition reaction, 36 additive, 36 additive name, 36 additivity of mass spectra , 37 additivity principle, 37 adduct, 37 adduct ion in mass spectrometry, 37 adhesional wetting, 38 adiabatic, 38 adiabatic electron transfer, 38 adiabatic ionization in mass spectrometry , 39 adiabatic lapse rate in atmospheric chemistry , 39 adiabatic photoreaction, 39 adiabatic transition-state theory, 39