Rotamers and Migration: Investigating the Dissociative Photoionization of Ethylenediamine

Abstract

The unimolecular dissociation of energy-selected ethylenediamine cations was studied by threshold photoelectron photoion coincidence spectroscopy (TPEPICO) in the photon energy range of 8.60-12.50 eV. Modeling the breakdown diagram and time-of-flight distributions with rigid activated complex RRKM theory yielded 0 K appearance energies for eight dissociation channels, leading to NH2CHCH2(+)(•) at 9.120 ± 0.010 eV, CH3C(NH2)2(+) at 9.200 ± 0.012 eV, NH2CHCH3(+) at 9.34 ± 0.08 eV, CH2NH2(+) at 9.449 ± 0.025 eV, CH2NH3(+) at 9.8 ± 0.1 eV, c-C2H4NH2(+) at 10.1 ± 0.1 eV, CH3NHCHCH2(+) at 10.2 ± 0.1 eV, and the reappearance of CH2NH2(+) at 10.2 ± 0.1 eV. The CBS-QB3-calculated pathways highlighted the influence of intramolecular hydrogen attractions on the dissociation processes, presenting novel isomers and low-energy van der Waals intermediates that led to fragments in good agreement with experimental results. While most of the dissociation channels take place through reverse barriers, the 0 K heat of formation of (•)CH2NH2 was determined to be 147.6 ± 3.7 kJ mol(-1), in excellent agreement with literature, and the 0 K heat of formation of CH2NH3(+) at 844 ± 10 kJ mol(-1) is the first experimentally measured value available and is in good agreement with theory.

Prediction of the product channels in the reaction of the methyl radical with fulminic acid

“…The CCSD(T)/CBS heat of reaction of 1.3 kcal/mol for the PR15 (H 2 + C 2 H 2 + NO) production is in excellent agreement with the experimental value of 1. , and −40.5 kcal/mol, respectively, thus lying within an error margin of ±1 kcal/mol (see Table 1). This was also found in other studies on gas phase reactions, [51][52][53][54][55][56][57][58][59][60][61] and shows that the CCSD(T)/6-311++G(3df,2p) level used here performs quite well, yielding reliable predicted relative energy values for structures on the same PES.…”

“…To confirm the reliability of the methods employed, the heats of reaction for HCNO + CH 3 are calculated at the three levels: B3LYP/6-311++G(3df,2p), CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++G(3df,2p), and CCSD(T)/CBS//B3LYP/6-311++G(3df,2p) and compared with available experimental data. [51][52][53][54][55][56][57][58][59][60][61] The (U)CCSD(T) energies extrapolated to the complete basis set (CBS) limit are also evaluated at these geometries as follows. The energy E(n) for each correlation consistent basis set, cc-PVnZ, with cardinal number n = 2 (DZ), 3 (TZ), and 4 (QZ) are combined using a mixed exponential/gaussian function of the form E(n…”

A twist on the reaction of the CN radical with methylamine in the interstellar medium: new hints from a state-of-the-art quantum-chemical study

“…However, as will be demonstrated, the reactive PES should be accurately investigated in order to understand which are the potential products in the harsh conditions typical of the ISM. Among them, there are two radical species poorly characterized in the literature (Dyke et al 1989;Wright & Miller 1996;Cour Jansen et al 1999;Muller et al 2016), namely CH 2 NH 2 and CH 3 NH, which warrant attention. Interestingly, the CH 2 NH + 2 cation has been recently investigated by highresolution rovibrational and pure rotational spectroscopy (Markus et al 2019).…”

Furfural: The Unimolecular Dissociative Photoionization Mechanism of the Simplest Furanic Aldehyde

“…Ab initio quantum chemical calculations were carried out using the Gaussian09 suite of programs . Potential energy surface (PES) scans were used to examine the reaction paths and to approximate the transition state (TS) structures by adjusting bond lengths and angles; the stationary points were calculated by taking the approximate TS structure and performing an optimization searching for a first-order saddle point. , Geometry optimizations of the minimum and saddle point structures of possible transition states on the PES were performed using the B3LYP/6-31G­(d) level of theory. − The reaction coordinate was followed by intrinsic reaction coordinate (IRC) , calculations from the transition states to verify the forward and reverse reaction mechanism. Any resulting minima from the IRC scans were recalculated to confirm the lowest energy structures at either end.…”

“…In this study, we present the unimolecular dissociative photoionization reactions of FAL recorded by imaging photoelectron photoion coincidence spectroscopy (iPEPICO) at the Swiss Light Source (SLS), Paul Scherrer Institute. − PEPICO has been accepted as a flexible tool to explore dissociation mechanisms and to determine highly accurate energetics for the dissociation of gas phase ions. − In iPEPICO, photoelectrons are kinetic energy analyzed with velocity map imaging and photoions are detected in delayed coincidence. The coincident electron kinetic energy and ion time-of-flight analysis permits the recording of photoion mass-selected threshold photoelectron spectra (ms-TPES) as a function of photon energy.…”