Simplified Multiple-Well Approach for the Master Equation Modeling of Blackbody Infrared Radiative Dissociation of Hydrated Carbonate Radical Anions

Abstract

Blackbody infrared radiative dissociation (BIRD) in a collision-free environment is a powerful method for the experimental determination of bond dissociation energies. In this work, we investigate temperature-dependent BIRD of CO 3•− (H 2 O) 1,2 at 250−330 K to determine water binding energies and assess the influence of multiple isomers on the dissociation kinetics. The ions are trapped in a Fourier-transform ion cyclotron resonance mass spectrometer, mass selected, and their BIRD kinetics are recorded at varying temperatures. Experimental BIRD rates as a function of temperature are fitted with rates obtained from master equation modeling (MEM), using the water binding energy as a fit parameter. MEM accounts for the absorption and emission of photons from black-body radiation, described with harmonic frequencies and infrared intensities from quantum chemical calculations. The dissociation rates as a function of internal energy are calculated by Rice−Ramsperger−Kassel−Marcus theory. Both single-well and multiple-well MEM approaches are used. Dissociation energies derived in this way from the experimental data are 56 ± 6 and 45 ± 3 kJ/mol for the first and second water molecules, respectively. They agree within error limits with the ones predicted by ab initio calculations done at the CCSD(T)/augcc-pVQZ//CCSD/aug-cc-pVDZ level of theory. We show that the multiple-well MEM approach described here yields superior results in systems with several low-lying minima, which is the typical situation for hydrated ions.

Magic cluster sizes of cationic and anionic sodium chloride clusters explained by statistical modeling of the complete phase space

“…Here, we use a modification of Rice-Ramsperger-Kassel-Marcus (RRKM) theory, [47][48][49] where we take into account all energetically accessible isomers i of cluster size x found in our quantum chemical calculations as well as all energetically accessible products j. We call this modification AWATAR for All Wells And Transition states Are Relevant.…”

“…To aid the interpretation of the fragmentation curves from SORI CID experiments, we calculate the density of states of individual isomers, as well as unimolecular dissociation rate constants k +/− x , n ( E ) for the dissociation of cluster size x by loss of (NaCl) n as a function of internal energy E according to eqn (1).Here, we use a modification of Rice–Ramsperger–Kassel–Marcus (RRKM) theory, 47–49 where we take into account all energetically accessible isomers i of cluster size x found in our quantum chemical calculations as well as all energetically accessible products j . We call this modification AWATAR for All Wells And Transition states Are Relevant.…”

“…The DOS and AWATAR calculations are performed with the program developed for master equation modeling, 47 which employs the Beyer–Swinehart algorithm 52 as described by Gilbert and Smith. 53 Single-point CCSD(T)/TZ//B3LYP-D3 and CCSD(T)/TZ//ωB97XD energies as well as unscaled B3LYP-D3/aug-cc-pVDZ and ωB97XD/aug-cc-pVDZ vibrational frequencies are used as input for the program, respectively.…”

Surface or Internal Hydration – Does It Really Matter?

“…16−18 Precise thermochemical information on the first solvation shell is obtained by guided ion beam (GIB) mass spectrometry in the Armentrout group, 19−23 while BIRD has been less frequently used for the measurement of water binding energies. 24,25 Ion spectroscopy in the infrared focuses on structural properties, with prominent contributions by Lee, Chang, and Niedner-Schatteburg, 26−28 Duncan, 3 Johnson, 29,30 Okumura, 31,32 Asmis, 33,34 Dopfer, 35 Ohashi, 36 Williams, 37−39 and Weber, 40 among others. Photoelectron spectroscopy provides insight into electronic structure and dynamics, as studied in the groups of Bowen, 41 Wang, 42 and Neumark.…”

“…Hydrated ions in the gas phase have been studied intensely since the 1970s, with seminal work such as the discovery of the magic (H 3 O) + (H 2 O) 20 cluster by Searcy and Fenn or the determination of hydration enthalpies with high-pressure mass spectrometry by the groups of Kebarle − and Castleman. − Precise thermochemical information on the first solvation shell is obtained by guided ion beam (GIB) mass spectrometry in the Armentrout group, − while BIRD has been less frequently used for the measurement of water binding energies. , Ion spectroscopy in the infrared focuses on structural properties, with prominent contributions by Lee, Chang, and Niedner-Schatteburg, − Duncan, Johnson, , Okumura, , Asmis, , Dopfer, Ohashi, Williams, − and Weber, among others. Photoelectron spectroscopy provides insight into electronic structure and dynamics, as studied in the groups of Bowen, Wang, and Neumark. , Reactivity of ionic water clusters has received considerable attention, in particular as model systems for atmospheric chemistry, pursued, among others, by the groups of Fehsenfeld and Ferguson, Castleman, , Okumura, and Bondybey and Niedner-Schatteburg. − …”