10.1021/jp064739s.s003 Andras Bodi Andras Bodi James P. Kercher James P. Kercher Curtis Bond Curtis Bond Patcharica Meteesatien Patcharica Meteesatien Bálint Sztáray Bálint Sztáray Tomas Baer Tomas Baer Photoion Photoelectron Coincidence Spectroscopy of Primary Amines RCH<sub>2</sub>NH<sub>2</sub> (R = H, CH<sub>3</sub>, C<sub>2</sub>H<sub>5</sub>, C<sub>3</sub>H<sub>7</sub>, <i>i</i>-C<sub>3</sub>H<sub>7</sub>):  Alkylamine and Alkyl Radical Heats of Formation by Isodesmic Reaction Networks American Chemical Society 2006 TPEPICO dissociation energies Photoion Photoelectron Coincidence Spectroscopy isodesmic reaction networks Δ fHo 298K 2H 3H alkylamine parent molecules W 1U levels ab initio values formation methylenimmonium ion RCH 2NH R ab initio results threshold photoelectron photoion coincidence spectroscopy Alkyl Radical Heats Isodesmic Reaction NetworksAlkylamines Primary Amines RCH 2NH kJ 3NH 2006-12-21 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Photoion_Photoelectron_Coincidence_Spectroscopy_of_Primary_Amines_RCH_sub_2_sub_NH_sub_2_sub_R_H_CH_sub_3_sub_C_sub_2_sub_H_sub_5_sub_C_sub_3_sub_H_sub_7_sub_i_i_i_C_sub_3_sub_H_sub_7_sub_Alkylamine_and_Alkyl_Radical_Heats_of_Formation_by_Isodesmic_Reacti/3040048 Alkylamines (RCH<sub>2</sub>NH<sub>2</sub>, R = H, CH<sub>3</sub>, C<sub>2</sub>H<sub>5</sub>, C<sub>3</sub>H<sub>7</sub>, <i>i</i>-C<sub>3</sub>H<sub>7</sub>) have been investigated by dissociative photoionization by threshold photoelectron photoion coincidence spectroscopy (TPEPICO). The 0 K dissociation limits (9.754 ± 0.008, 9.721 ± 0.008, 9.702 ± 0.012, and 9.668 ± 0.012 eV for R = CH<sub>3</sub>, C<sub>2</sub>H<sub>5</sub>, C<sub>3</sub>H<sub>7</sub>, <i>i</i>-C<sub>3</sub>H<sub>7</sub>, respectively) have been determined by preparing energy-selected ions and collecting the fractional abundances of parent and daughter ions. All alkylamine cations produce the methylenimmonium ion, CH<sub>2</sub>NH<sub>2</sub><sup>+</sup>, and the corresponding alkyl free radical. Two isodesmic reaction networks have also been constructed. The first one consists of the alkylamine parent molecules, and the other of the alkyl radical photofragments. Reaction heats within the isodesmic networks have been calculated at the CBS-APNO and W1U levels of theory. The two networks are connected by the TPEPICO dissociation energies. The heats of formation of the amines and the alkyl free radicals are then obtained by a modified least-squares fit to minimize the discrepancy between the TPEPICO and the <i>ab initio</i> values. The analysis of the fit reveals that the previous experimental heats of formation are largely accurate, but certain revisions are suggested. Thus, Δ<sub>f</sub><i>H</i><sup>o</sup><sub>298K</sub><i><sup> </sup></i><sup></sup>[CH<sub>3</sub>NH<sub>2</sub>(g)] = −21.8 ± 1.5 kJ mol<sup>-1</sup>, Δ<sub>f</sub><i>H</i><sup>o</sup><sub>298K</sub>[C<sub>2</sub>H<sub>5</sub>NH<sub>2</sub>(g)] = −50.1 ± 1.5 kJ mol<sup>-1</sup>, Δ<sub>f</sub><i>H</i><sup>o</sup><sub>298K</sub>[C<sub>3</sub>H<sub>7</sub>NH<sub>2</sub>(g)] = −70.8 ± 1.5 kJ mol<sup>-1</sup>, Δ<sub>f</sub><i>H</i><sup>o</sup><sub>298K</sub>[C<sub>3</sub>H<sub>7</sub><sup>•</sup>] = 101.3 ± 1 kJ mol<sup>-1</sup>, and Δ<sub>f</sub><i>H</i><sup>o</sup><sub>298K</sub>[<i>i</i>-C<sub>3</sub>H<sub>7</sub><sup>•</sup>] = 88.5 ± 1 kJ mol<sup>-1</sup>. The TPEPICO and the <i>ab initio</i> results for butylamine do not agree within 1 kJ mol<sup>-1</sup>; therefore, no new heat of formation is proposed for butylamine. It is nevertheless indicated that the previous experimental heats of formation of methylamine, propylamine, butylamine, and isobutylamine may have been systematically underestimated. On the other hand, the error in the ethyl radical heat of formation is found to be overestimated and can be decreased to ± 1 kJ mol<sup>-1</sup>; thus, Δ<sub>f</sub><i>H</i><sup>o</sup><sub>298K</sub>[C<sub>2</sub>H<sub>5</sub>·] = 120.7 ± 1 kJ mol<sup>-1</sup>. On the basis of the data analysis, the heat of formation of the methylenimmonium ion is confirmed to be Δ<sub>f</sub><i>H</i><sup>o</sup><sub>298K</sub>[CH<sub>2</sub>NH<sub>2</sub><sup>+</sup>] = 750.3 ± 1 kJ mol<sup>-1</sup>.