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.

Transition metals are important in various industrial applications including catalysis. Due to the current concentration of CO 2 in the atmosphere, various ways for its capture and utilization are investigated. Here, we study the activation of CO 2 and H 2 O at [NbO 3 ] − in the gas phase using a combination of infrared multiple photon dissociation spectroscopy and density functional theory calculations. In the experiments, Fourier-transform ion cyclotron resonance mass spectrometry is combined with tunable IR laser light provided by the intracavity free-electron laser FELICE or optical parametric oscillator-based table-top laser systems. We present spectra of [NbO 3 ] − , [NbO 2 (OH) 2 ] − , [NbO 2 (OH) 2 ] − (H 2 O) and [NbO(OH) 2 (CO 3 )] − in the 240–4000 cm –1 range. The measured spectra and observed dissociation channels together with quantum chemical calculations confirm that upon interaction with a water molecule, [NbO 3 ] − is transformed to [NbO 2 (OH) 2 ] − via a barrierless reaction. Reaction of this product with CO 2 leads to [NbO(OH) 2 (CO 3 )] − with the formation of a [CO 3 ] moiety.

Judit Zádor opened a discussion of the paper by Michael P. Burke: One outcome of this work is that rate coefficients can have a dependence that goes beyond just pressure and temperature. Is there a suitable formalism by which such dependencies could be represented in phenomenological kinetic models, such as the ones that are used to model combustion? Michael P. Burke answered: Yes, the rate coefficients can also depend on composition in addition to pressure and temperature, where the composition dependence arises not only from the composition dependence of the energy transfer terms but also the composition dependence of the bimolecular reaction terms. My group and I have developed suitable ways of representing the composition dependence of rate coefficients due to energy transfer effects (described in ref. 1-5 below), though it remains an open question how to best represent the additional composition dependence stemming from the reaction term in phenomenological kinetic models. 1 L. Lei and M. P. Burke, Dynamically evaluating mixture effects on multi-channel reactions in ames: A case study for the CH 3 + OH reaction, Proc. Combust. Inst., 2021, 38, 433-440. 2 L. Lei and M. P. Burke, Mixture rules and falloff are now major uncertainties in experimentally derived rate parameters for H + O 2 (+M) 4 HO 2 (+M), Combust. Flame, 2020, 213, 467-474. 3 L. Lei and M. P. Burke, Bath gas mixture effects on multi-channel reactions: insights and representations for systems beyond single-channel reactions,