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>.