Photoion Photoelectron Coincidence Spectroscopy of Primary Amines RCH2NH2 (R = H, CH3, C2H5, C3H7, i-C3H<

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• 作者：Andras Bodi ; James P. Kercher ; Curtis Bond ; Patcharica Meteesatien ; Bá ; lint Sztá ; ray ; Tomas Baer
• 刊名：Journal of Physical Chemistry A
• 出版年：2006
• 出版时间：December 21, 2006
• 年：2006
• 卷：110
• 期：50
• 页码：13425 - 13433
• 全文大小：231K
• 年卷期：v.110,no.50(December 21, 2006)
• ISSN：1520-5215

文摘

Alkylamines (RCH₂NH₂, R = H, CH₃, C₂H₅, C₃H₇, i-C₃H₇) have been investigated by dissociativephotoionization by threshold photoelectron photoion coincidence spectroscopy (TPEPICO). The 0 K dissociationlimits (9.754 ± 0.008, 9.721 ± 0.008, 9.702 ± 0.012, and 9.668 ± 0.012 eV for R = CH₃, C₂H₅, C₃H₇,i-C₃H₇, respectively) have been determined by preparing energy-selected ions and collecting the fractionalabundances of parent and daughter ions. All alkylamine cations produce the methylenimmonium ion, CH₂NH₂⁺, 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 oftheory. The two networks are connected by the TPEPICO dissociation energies. The heats of formation ofthe amines and the alkyl free radicals are then obtained by a modified least-squares fit to minimize thediscrepancy between the TPEPICO and the ab initio values. The analysis of the fit reveals that the previousexperimental heats of formation are largely accurate, but certain revisions are suggested. Thus, _fH^o_298K [CH₃NH₂(g)] = -21.8 ± 1.5 kJ mol^-1, _fH^o_298K[C₂H₅NH₂(g)] = -50.1 ± 1.5 kJ mol^-1, _fH^o_298K[C₃H₇NH₂(g)] =-70.8 ± 1.5 kJ mol^-1, _fH^o_298K[C₃H₇] = 101.3 ± 1 kJ mol^-1, and _fH^o_298K[i-C₃H₇] = 88.5 ± 1 kJ mol^-1.The TPEPICO and the ab initio results for butylamine do not agree within 1 kJ mol^-1; therefore, no new heatof formation is proposed for butylamine. It is nevertheless indicated that the previous experimental heats offormation of methylamine, propylamine, butylamine, and isobutylamine may have been systematicallyunderestimated. On the other hand, the error in the ethyl radical heat of formation is found to be overestimatedand can be decreased to ± 1 kJ mol^-1; thus, _fH^o_298K[C₂H₅·] = 120.7 ± 1 kJ mol^-1. On the basis of the dataanalysis, the heat of formation of the methylenimmonium ion is confirmed to be _fH^o_298K[CH₂NH₂⁺] = 750.3± 1 kJ mol^-1.