A Common Bottleneck for Metal Oxidation by Molecular Oxygen Across Size Regimes: Kinetics of Atomic Lanthanide Cations (La-Lu) with O.

Kinetics of the lanthanide cations (Ln = La-Lu excluding ) reacting with molecular oxygen were measured in a selected-ion flow tube apparatus from 300 to 600 K. Where exothermic, these reactions occur efficiently, producing LnO + O. The reactions display positive temperature dependences consistent with Arrhenius equation behavior and show small activation energies (0-2 kJ mol) that are strongly correlated to promotion energies of the Ln atoms.

Kinetics for the Reactions of Ar, O, and NO with Isoprene (2-Methyl-1,3-butadiene) as a Function of Temperature (300-500 K).

Rate constants and product branching fractions were measured for reactions of Ar, O, and NO with isoprene (2-methyl-1,3-butadiene CH) as a function of temperature. The rate constants are large (∼2 × 10 cm s) and increase with temperature, exceeding the ion-dipole/induced dipole capture rate. Adding a hard sphere term to the collision rate provides a more useful upper limit and predicts the positive temperature dependences.

Activation of Methane by Zr: A Deep-Dive into the Potential Surface via Pressure- and Temperature-Dependent Kinetics with Statistical Modeling.

The kinetics of Zr + CH are measured using a selected-ion flow tube apparatus over the temperature range 300-600 K and the pressure range 0.25-0.60 Torr.

Kinetics for the Reactions of HO(HO) with Isoprene (2-Methyl-1,3-butadiene) as a Function of Temperature (300-500 K).

We report kinetics studies of HO(HO) with isoprene (2-methyl-1,3-butadiene, CH) as a function of temperature (300-500 K) measured using a flowing afterglow-selected ion flow tube. Results are supported by density functional (DFT) calculations at the B3LYP/def2-TZVP level. HO ( = 0) reacts with isoprene near the collision limit exclusively via proton transfer to form CH.

Excited-State N Atoms Transform Aromatic Hydrocarbons into -Heterocycles in Low-Temperature Plasmas.

The direct formation of -heterocycles from aromatic hydrocarbons has been observed in nitrogen-based low-temperature plasmas; the mechanism of this unusual nitrogen-fixation reaction is the topic of this paper. We used homologous aromatic compounds to study their reaction with reactive nitrogen species (RNS) in a dielectric barrier discharge ionization (DBDI) source. Toluene (CH) served as a model compound to study the reaction in detail, which leads to the formation of two major products at "high" plasma voltage: a nitrogen-replacement product yielding protonated methylpyridine (CHN) and a protonated nitrogen-addition (CHN) product.

Effect of Intersystem Crossings on the Kinetics of Thermal Ion-Molecule Reactions: Ti + O, CO, and NO.

A selected-ion flow tube apparatus has been used to measure rate constants and product branching fractions of Ti reacting with O, CO, and NO over the range of 200-600 K. Ti + O proceeds at near the Langevin capture rate constant of 6-7 × 10 cm s at all temperatures to yield TiO + O. Reactions initiated on doublet or quartet surfaces are formally spin-allowed; however, the 50% of reactions initiated on sextet surfaces must undergo an intersystem crossing (ISC).

Sublimation Kinetics for Individual Graphite and Graphene Nanoparticles (NPs): NP-to-NP Variations and Evolving Structure-Kinetics and Structure-Emissivity Relationships.

A single nanoparticle (NP) mass spectrometry method was used to measure sublimation rates as a function of nanoparticle temperature (T) for sets of individual graphite and graphene NPs. Initially, the NP sublimation rates were ∼400 times faster than those for bulk graphite, and there were large NP-to-NP variations. Over time, the rates slowed substantially, though they remained well above the bulk rate.

Thermal emission spectroscopy for single nanoparticle temperature measurement: optical system design and calibration.

We discuss the design of an optical system that allows measurement of 600-1650 nm emission spectra for individual nanoparticles (NPs), laser-heated in an electrodynamic trap in controlled atmospheres. An approach to calibration of absolute intensity versus wavelength for very low emission intensities is discussed, and examples of NP graphite and carbon black spectra are used to illustrate the methodology.

Single Nanoparticle Mass Spectrometry as a High Temperature Kinetics Tool: Sublimation, Oxidation, and Emission Spectra of Hot Carbon Nanoparticles.

In single nanoparticle mass spectrometry, individual charged nanoparticles (NPs) are trapped in a quadrupole ion trap and detected optically, allowing their mass, charge, and optical properties to be monitored continuously. Previous experiments of this type probed NPs that were either fluorescent or large enough to detect by light scattering. Alternatively, small NPs can be heated to temperatures where thermally excited emission is strong enough to allow detection, and this approach should provide a new tool for measurements of sublimation and surface reaction kinetics of materials at high temperatures.

Photoluminescence of charged CdSe/ZnS quantum dots in the gas phase: effects of charge and heating on absorption and emission probabilities.

Gas phase spectral measurements for CdSe/ZnS core/shell nanocrystal quantum dots (QDs) before and after heating with both infrared (CO2) and visible lasers are reported. As-trapped QDs are spectrally similar to the same QDs in solution; however their photoluminescence (PL) intensities are very low, at least partly due to low absorption cross sections. After heating, the PL intensities brighten by factors ranging from ∼4 to 1800 depending on the QD size and pump laser wavelength.