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Experimental Proton Affinities

Proton affinities in kJ mol-1
Molecule name State Conformation Proton Affinity Uncertainity Product molecule Product name reference commment
H- Hydrogen atom anion 2S Kh 1675.3   H2 Hydrogen diatomic webbook
H Hydrogen atom 1S Kh 257.7   H2+ Hydrogen cation webbook derived from webbook
He Helium atom 1S Kh 177.8   HeH+ Helium hydride cation webbook
N Nitrogen atom 4S Kh 342.2   NH+ imidogen cation webbook
O Oxygen atom 3S Kh 485.2   OH+ hydoxyl cation webbook
F- Fluorine atom anion 1S Kh 1555.0 5.0 HF Hydrogen fluoride webbook
F Fluorine atom 2P Kh 340.1   HF+ hydrogen fluoride cation webbook
Ne Neon atom 1S Kh 198.8   NeH+ neon hydrogen cation webbook
Mg Magnesium atom 1S Kh 819.6   MgH+ magnesium monohydride cation webbook
Si Silicon atom 3P Kh 837.0   SiH+ silicon monohydride cation webbook
P Phosphorus atom 4S Kh 626.8   PH+ phosphorus monohydride cation webbook
S Sulfur atom 3P Kh 664.3   HS+ sulfur monohydride cation webbook
Cl- Chlorine atom anion 1S Kh 1394.9   HCl Hydrogen chloride webbook
Cl Chlorine atom 2P Kh 513.6   HCl+ hydrogen chloride cation webbook
Ar Argon atom 1S Kh 369.2   ArH+ Argon hydride cation webbook
Sc Scandium atom 2D Kh 914.0   ScH+ Scandium monohydride cation webbook
Br- Bromine atom anion 1S Kh 1353.7 0.2 HBr hydrogen bromide webbook
Br Bromine atom 2P Kh 554.4   HBr+ hydrogen bromide cation webbook
Kr Krypton atom 1S Kh 424.3 3.3 KrH+ Protonated Krypton 1980Boh/Mac:4976
I- Iodine atom anion 1S Kh 1315.2 0.1 HI Hydrogen iodide webbook
Xe Xenon atom 1S Kh 493.7 3.8 XeH+ Xenon, protonated 1980Boh/Mac:4976
H2 Hydrogen diatomic 1Σg D∞h 422.3   H3+ hydrogen trimer cation webbook
CN- cyanide anion 1Σ C∞v 1466.5 0.7 HCN Hydrogen cyanide webbook
CN Cyano radical 2Σ C∞v     HCN+ hydrogen cyanide cation  
CN Cyano radical 2Σ C∞v     HNC+ hydrogen isocyanide cation  
N2 Nitrogen diatomic 1Σg D∞h 493.8   NNH+ Dinitrogen monohydride cation webbook
OH- hydroxide anion 1Σ C∞v 1633.1 0.0 H2O Water webbook
CO Carbon monoxide 1Σ C∞v 594.0   HCO+ Formyl cation webbook HCO+
CO Carbon monoxide 1Σ C∞v 426.3   COH+ Carbon Monoxide, protonated webbook COH+
NO Nitric oxide 2Π C∞v 531.8   HNO+ Nitrosyl hydride cation webbook
NO Nitric oxide 2Π C∞v     NOH+ O-protonated nitric oxide  
O2 Oxygen diatomic 3Σg D∞h 421.0   HO2+ Hydroperoxy cation webbook
HF Hydrogen fluoride 1Σ C∞v 484.0   H2F+ dihydrogen fluoride cation webbook
F2 Fluorine diatomic 1Σg D∞h 332.0   H2F+ dihydrogen fluoride cation webbook
PO Phosphorus monoxide 2Π C∞v 682.0   HPO+ Hydrogen phosphorus oxide cation webbook
HS- mercapto anion 1Σ C∞v 1470.0 3.0 H2S Hydrogen sulfide webbook
CS carbon monosulfide 1Σ C∞v 791.5   HCS+ Thioformyl cation webbook
HCl Hydrogen chloride 1Σ C∞v 556.9   H2Cl+ dihydrogen monochloride cation webbook
Cl2 Chlorine diatomic 1Σg D∞h 549.8 4.2 Cl2H+ Chlorine, protonated 1998Cac/deP:10560
HSe- selenium monohydride anion 1Σ C∞v 1428.8 2.9 H2Se Hydrogen selenide webbook
HBr hydrogen bromide 1Σ C∞v 584.2   H2Br+ protonated hydrogen bromide webbook
HI Hydrogen iodide 1Σ C∞v 627.5   H2I+ Iodonium webbook
HNC hydrogen isocyanide 1Σ C∞v 772.3   H2CN+ hydrocyanonium cation webbook
HNC hydrogen isocyanide 1Σ C∞v     CNH2+ N-protonated hydrogen isocyanide  
HCN Hydrogen cyanide 1Σ C∞v 712.9   H2CN+ hydrocyanonium cation webbook
H2O Water 1A1 C2v 691.0   H3O+ hydronium cation webbook
HCO Formyl radical 2A' Cs 636.0   H2CO+ formaldehyde cation webbook
CO2 Carbon dioxide 1Σg D∞h 540.5   HOCO+ Hydrocarboxyl cation webbook
N2O Nitrous oxide 1Σ C∞v 575.2   NNOH+ Nitrous Oxide, O-protonated webbook O-protonated
N2O Nitrous oxide 1Σ C∞v 549.8   HNNO+ Nitrous oxide, N-protonated webbook N-protonated
NO2 Nitrogen dioxide 2A1 C2v 591.0   HNO2+ nitrous acid cation webbook
O3 Ozone 1A1 Cs 625.5   O3H+ protonated ozone webbook
H2S Hydrogen sulfide 1A1 C2v 705.0   H3S+ Sulfonium cation webbook
SO2 Sulfur dioxide 1A1 C2v 672.3   SO2H+ protonated sulfur dioxide webbook
CS2 Carbon disulfide 1Σg D∞h 681.9   CS2H+ Carbon disulfide, protonated webbook
KOH Potassium hydroxide 1Σ C∞v 1101.8   KOH2+ Potassium hydroxide, protonated webbook
H2Se Hydrogen selenide 1A1 C2v 707.8   H3Se+ Hydrogen Selenide, protonated webbook
C2H2 Acetylene 1Σg D∞h 641.4   C2H3+ vinyl cation webbook
NH3 Ammonia 1A1 C3v 853.6   NH4+ ammonium cation webbook
HN3 hydrogen azide 1A' Cs 756.0   HNNNH+ 1,2-Triazadienium webbook
H2CO Formaldehyde 1A1 C2v 712.9   CH2OH+ hydroxymethyl cation webbook
H2O2 Hydrogen peroxide 1A C2 674.5   H3O2+ hydrogen peroxide, protonated webbook
HCO2- formate anion 1A1 C2v 1449.0 5.0 HCOOH Formic acid webbook
NO3- nitrate anion 1A1' D3h 1357.7 0.8 HNO3 Nitric acid webbook
NF3 Nitrogen trifluoride 1A1 C3v 568.4   NF3H+ protonated nitrogen trifluoride webbook
H2CS Thioformaldehyde 1A1 C2v 759.7   H2CSH+ Thioformaldehyde, protonated webbook
C2H3- vinyl anion 1A' Cs 1704.0 9.0 C2H4 Ethylene webbook
CH2NH Methanimine 1A' Cs 852.9   CH2NH2+ methyleneamine cation webbook
CH2NN diazomethane 1A1 C2v 858.9   NCNH3+ Cyanamide, protonated webbook
NH2CN cyanamide 1A' Cs 805.6   NH2CNH+ cyanamide, cn protonated webbook
CH3O- methoxy anion 1A1 C3v 1598.0 8.0 CH3OH Methyl alcohol webbook
NH2OH hydroxylamine 1A' Cs 810.4 8.4 NH3OH+ N-protonated hydroxylamine 1995Ang/Asc:6551
CH2CO Ketene 1A1 C2v 825.3   CH3CO+ acetyl cation webbook
CH2CO Ketene 1A1 C2v     CH2COH+ ketene, protonated  
HCOOH Formic acid 1A' Cs 742.0   CH3OO+ methylperoxy cation webbook
HNO3 Nitric acid 1A' Cs 751.4   H2NO3+ Nitric Acid, Protonated webbook
CH3Cl Methyl chloride 1A1 C3v 647.3   CH3ClH+ methyl chloride, protonated webbook
C2H4 Ethylene 1Ag D2h 680.5   C2H5+ Ethyl cation webbook
N2H4 Hydrazine 1A C2 853.2   N2H5+ protonated hydrazine webbook
CH3OH Methyl alcohol 1A' Cs 754.3   CH3OH2+ Methanol, protonated webbook
CHONH2 formamide 1A' Planar 822.2   NH2CHOH+ Formamide, O-protonated webbook
CH3SH Methanethiol 1A' Cs 773.4   CH3SH2+ protonated methylsulfide webbook
HSO4- bisulfate anion 1A' Cs 1295.0 11.0 H2SO4 Sulfuric acid webbook
C2H5- Ethyl anion 1A' Cs 1758.0 8.4 C2H6 Ethane webbook
C3H4 cyclopropene 1A1 C2v 818.5   C3H5+ Allyl cation webbook
CH3CCH propyne 1A' C3v 748.0   C3H5+ Allyl cation webbook
CH2CCH2 allene 1A1 D2d 775.3   C3H5+ Allyl cation webbook
CH3NH2 methyl amine 1A' Cs 899.0   CH3NH3+ protonated methylamine webbook
CH3N3 methyl azide 1A' Cs 833.0   CH3NHN2+ methyl azide, protonated webbook
CH3CHO Acetaldehyde 1A' Cs 768.5   CH3CHOH+ acetaldehyde, protonated webbook
C2H4O Ethylene oxide 1A1 C2v 774.2   C2H4OH+ ethylene oxide, protonated 1998Hun/Lia:413
CH3COO- acetate anion 1A' eclipsed 1457.0 5.9 CH3COOH Acetic acid webbook
CF3COO- trifluoro acetate anion 1A' Cs 1355.0 12.0 CF3COOH trifluoroacetic acid webbook
CH3PH2 Methyl phosphine 1A' Cs 851.5   CH3PH3+ methyl phosphine, protonated webbook
C2H6 Ethane 1A1g D3d 596.3   C2H7+ Ethane, protonated webbook
C2H5N Aziridine 1A' C1 905.5   C2H5NH+ Protonated Aziridine webbook
CH2CHNH2 aminoethene 1A C1 898.9   C2H5NH+ Protonated Aziridine webbook
NH2CONH2 Urea 1A C2 868.4 2.5 H2NCOHNH2+ urea, protonated webbook
CH2CHCH3 Propene 1A' Cs 751.6   CH3CHCH3+ Isopropyl cation webbook
C3H6 Cyclopropane 1A1' D3h 750.3   CH3CHCH3+ Isopropyl cation webbook
CH5N3 Guanidine 1A C1 986.3   CH6N3+ guanidinium webbook
CH2ClCH2OH 2-Chloroethanol 1A' Cs 766.1   CH2ClCH2OH2+ 2-chloroethanol, protonated webbook
CH3NHCH3 Dimethylamine 1A' Cs 929.5   (CH3)2NH2+ dimethylammonium cation webbook
CH3CH2NH2 Ethylamine 1A' Cs 912.0   CH3CH2NH3+ ethylamine, protonated webbook
C4H5N Pyrrole 1A1 C2v 875.4   C4H6N+ pyrrole, protonated webbook
CH3COCH3 Acetone 1A1 C2v 812.0   CH3COHCH3+ acetone, protonated webbook
C3H6O Oxetane 1A1 C2v 801.3   CH3COHCH3+ acetone, protonated webbook
C5H5N Pyridine 1A1 C2v 930.0   C5H6N+ Pyridinium webbook
C6H6 Benzene 1A1g D6h 750.4   C6H7+ benzene, protonated webbook
NH2CH2CH2CH3 1-Propanamine 1A' Cs 917.8   C3H7NH3+ n-propylamine, protonated webbook
N(CH3)3 Trimethylamine 1A1 C3v 948.9   (CH3)3NH+ protonated trimethyl amine webbook

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squib reference DOI
1980Boh/Mac:4976 DK Bohme, GI Mackay, HI Schiff "Determination of proton affinities from the kinetics of proton transfer reactions. VII. The proton affinities of O2, H2, Kr, O, N2, Xe, CO2, CH4, N2O, and CO" J. Chem. Phys. 73(10), 1980, 4976 10.1063/1.439975
1995Ang/Asc:6551 F Angelelli, M Aschi, F Cacace, F Pepi, G de Petris "Gas-Phase Reactivity of Hydroxylamine toward Charged Electrophiles. A Mass Spectrometric and Computational Study of the Protonation of Methylation of H2NOH" J. Phys. Chem. 1995, 99, 6551-6556 10.1021/j100017a041
1998Cac/deP:10560 F Cacace, G dePetris, F Pepi, M Rosi, A Sgamellotti "Elemental Chlorine and Chlorine Fluoride: Theoretical and Experimental Proton Affinity and the Gas Phase Chemistry of Cl2H+ and FClH+ Ions" J. Phys. Chem. A 1998, 102, 10560-10567 10.1021/jp9831379
1998Hun/Lia:413 EPL Hunter, SG Lias "Evaluated Gas Phase Basicities and Proton Affinities of Molecules: An Update" J. Phys. Chem. Ref. Data Vol. 27, No. 3, pp. 413-656 (1998) 10.1063/1.556018
webbook NIST Chemistry Webbook ( 10.18434/T4D303

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