Measurement of Time Dependent Product Branching Ratios Indicates Two-State Reactivity in Metal Mediated Chemical Reactions

For several decades, the influence of Two State Reactivity (TSR) has been implicated in a host of reactions, but has lacked a stand-alone, definitive experimental kinetic signature identifying its occurrence....

Experimental and Computational Studies on the Reactivity of Methanimine Radical Cation (H2CNH+•) and its Isomer Aminomethylene (HCNH2+•) With C2H2

Experimental and theoretical studies are presented on the reactivity of the radical cation isomers H2CNH+• (methanimine) and HCNH2+• (aminomethylene) with ethyne (C2H2). Selective isomer generation is performed via dissociative photoionization of suitable neutral precursors as well as via direct photoionization of methanimine. Reactive cross sections (in absolute scales) and product branching ratios are measured as a function of photon and collision energies. Differences between isomers’ reactivity are discussed in light of ab-initio calculations of reaction mechanisms. The major channels, for both isomers, are due to H atom elimination from covalently bound adducts to give [C3NH4]+. Theoretical calculations show that while for the reaction of HCNH2+• with acetylene any of the three lowest energy [C3NH4]+ isomers can form via barrierless and exothermic pathways, for the H2CNH+• reagent the only barrierless pathway is the one leading to the production of protonated vinyl cyanide (CH2CHCNH+), a prototypical branched nitrile species that has been proposed as a likely intermediate in star forming regions and in the atmosphere of Titan. The astrochemical implications of the results are briefly addressed.

Mechanism and Kinetics of the Oxidation of 1,3-Butadien-1-yl (n-C4H5): A Theoretical Study

Ab initio CCSD(T)-F12/cc-pVTZ-f12//B3LYP/6-311G(d,p) calculations of the C4H5O2 potential energy surface have been combined with Rice-Ramsperger-Kassel-Marcus Master Equation (RRKM-ME) calculations of temperature- and pressure-dependent rate constants and product branching ratios to...

The H2+ + HD reaction at low collision energies: H3+/H2D+ branching ratio and product-kinetic-energy distributions

The reactions between H2+ and HD forming H3+ + D as well as H2D+ + H were measured at collision energies between 0 and kB·30 K and a resolution of 75 mK and the H3+/H2D+ product branching ratio and the product kinetic-energy distribution were determined.

Excited-State Vibration-Polariton Transitions and Dynamics in Nitroprusside

<div> <div> <div> <p>Strong cavity coupling to molecular vibrations creates vibration-polaritons capable of modifying chemical reaction kinetics, product branching ratios, and charge transfer equilibria. However, the mechanisms impacting these molecular processes remain elusive. Furthermore, even basic elements determining the spectral properties of polaritons, such as selection rules, transition moments, and lifetimes, are poorly understood. Here, we use two-dimensional infrared and filtered pump–probe spectroscopy to report clear spectroscopic signatures and relaxation dynamics of excited vibration-polaritons formed from the cavity- coupled NO band of nitroprusside. We apply a multi-level quantum Rabi model that predicts transition frequencies and strengths that agree very well with our experiment. Notably, the polariton features decay ~3-4 times slower than the polariton dephasing time, indicating that they support incoherent population, a consequence of their partial matter character. Understanding the factors determining polariton population and dephasing lifetimes will impact polariton-modified energy transfer, photophysics, and chemistry. </p> </div> </div> </div>

Excited-State Vibration-Polariton Transitions and Dynamics in Nitroprusside

<div> <div> <div> <p>Strong cavity coupling to molecular vibrations creates vibration-polaritons capable of modifying chemical reaction kinetics, product branching ratios, and charge transfer equilibria. However, the mechanisms impacting these molecular processes remain elusive. Furthermore, even basic elements determining the spectral properties of polaritons, such as selection rules, transition moments, and lifetimes, are poorly understood. Here, we use two-dimensional infrared and filtered pump–probe spectroscopy to report clear spectroscopic signatures and relaxation dynamics of excited vibration-polaritons formed from the cavity- coupled NO band of nitroprusside. We apply a multi-level quantum Rabi model that predicts transition frequencies and strengths that agree very well with our experiment. Notably, the polariton features decay ~3-4 times slower than the polariton dephasing time, indicating that they support incoherent population, a consequence of their partial matter character. Understanding the factors determining polariton population and dephasing lifetimes will impact polariton-modified energy transfer, photophysics, and chemistry. </p> </div> </div> </div>

Barrierless Reactions of Three Benzonitrile Radical Cations with Ethylene

Reactions of three protonated benzonitrile radical cations with ethylene are investigated. Product branching ratios and reaction kinetics, measured using ion-trap mass spectrometry, are reported and mechanisms are developed with support from quantum chemical calculations. Reactions proceed via pre-reactive van der Waals complexes with no energy barrier (above the reactant energy) and form radical addition and addition–elimination product ions. Rate coefficients are 4-dehydrobenzonitrilium: 1.72±0.01×10−11 cm3 molecule−1 s−1, 3-dehydrobenzonitrilium: 1.85±0.01×10−11 cm3 molecule−1 s−1, and 2-dehydrobenzonitrilium: 5.96±0.06×10−11 cm3 molecule−1 s−1 (with±50% absolute uncertainty). A ring-closure mechanism involving the protonated nitrile substituent is proposed for the 2-dehydrobenzonitrilium case and suggests favourable formation of the protonated indenimine cation.