More Like this

1. Reactions of Aluminum Oxide Cluster Cations with Ethane: A Mass‐Spectrometric and Vibrational Spectroscopy Study

   https://doi.org/10.1002/cphc.202400427  

   Phasuk, Apakorn; Metz, Ricardo_B (November 2024, ChemPhysChem)

   Abstract The pathways for the reactions of aluminum oxide cluster ions with ethane have been measured. For selected ions (Al₂O⁺, Al₃O₂⁺, Al₃O₄⁺, Al₄O₇⁺) the structure of the collisionally‐stabilized reaction intermediates were explored by measuring the photodissociation vibrational spectra from 2600 cm⁻¹–3100 cm⁻¹. Density functional theory was used to calculate features of the potential energy surfaces for the reactions and the vibrational spectra of intermediates. Generally, more than one isomer contributes to the observed spectrum. The oxygen‐deficient clusters Al₂O⁺and Al₃O₂⁺have large C−H activation barriers, so only the entrance channel complexes in which intact C₂H₆binds to aluminum are observed. This interaction leads to a substantial (~200 cm⁻¹) red shift of the C−H symmetric stretch in ethane, indicating significant weakening of the proximal C−H bonds. In Al₃O₄⁺, the complex formed by interactions with three C₂H₆is investigated and, in addition to entrance channel complexes, the C−H activation intermediate Al₃O₄H⁺(C₂H₅)(C₂H₆)₂is observed. For oxygen‐rich Al₄O₇⁺, the C₂H₆is favored to bind at an aluminum site far from the reactive superoxide group, reducing the reactivity. As expected, oxygen‐rich species and open‐shell cluster ions have smaller barriers for C−H bond activation, except for Al₃O₄⁺which is predicted and observed to be reactive. 

   more » « less
2. Infrared spectroscopy of ions and ionic clusters upon ionization of ethane in helium droplets

   https://doi.org/10.1063/5.0091819  

   Erukala, Swetha; Feinberg, Alexandra J.; Moon, Cheol Joo; Choi, Myong Yong; Vilesov, Andrey F. (May 2022, The Journal of Chemical Physics)

   Helium droplets are unique hosts for isolating diverse molecular ions for infrared spectroscopic experiments. Recently, it was found that electron impact ionization of ethylene clusters embedded in helium droplets produces diverse carbocations containing three and four carbon atoms, indicating effective ion–molecule reactions. In this work, similar experiments are reported but with the saturated hydrocarbon precursor of ethane. In distinction to ethylene, no characteristic bands of larger covalently bound carbocations were found, indicating inefficient ion–molecule reactions. Instead, the ionization in helium droplets leads to formation of weaker bound dimers, such as (C₂H₆)(C₂H₄)⁺, (C₂H₆)(C₂H₅)⁺, and (C₂H₆)(C₂H₆)⁺, as well as larger clusters containing several ethane molecules attached to C₂H₄⁺, C₂H₅⁺, and C₂H₆⁺ionic cores. The spectra of larger clusters resemble those for neutral, neat ethane clusters. This work shows the utility of the helium droplets to study small ionic clusters at ultra-low temperatures. 

   more » « less
3. Direct D-atom Incorporation in Radicals: An Overlooked Pathway for Deuterium Fractionation

   https://doi.org/10.3847/1538-4357/acac1d  

   Dias, Nureshan; Gurusinghe, Ranil M.; Broderick, Bernadette M.; Millar, Tom J.; Suits, Arthur G. (February 2023, The Astrophysical Journal)

   Abstract Direct D-H exchange in radicals is investigated in a quasi-uniform flow employing chirped-pulse millimeter-wave spectroscopy. Inspired by the H-atom catalyzed isomerization of C₃H₂reported in our previous study, D-atom reactions with the propargyl (C₃H₃) radical and its photoproducts were investigated. We observed very efficient D-atom enrichment in the photoproducts through an analogous process of D addition/H elimination to C₃H₂isomers occurring at 40 K or below. Cyclic C₃HD is the only deuterated isomer observed, consistent with the expected addition/elimination yielding the lowest energy product. The other expected addition/elimination product, deuterated propargyl, is not directly detected, although its presence is inferred by the observations in the latter part of the flow. There, in the high-density region of the flow, we observed both isotopomers of singly deuterated propyne attributed to stabilization of the H+C₃H₂D or D+C₃H₃adducts. The implications of these observations for the deuterium fractionation of hydrocarbon radicals in astrochemical environments is discussed with the support of a monodeuterated chemical kinetic model. 

   more » « less
4. Structure and vibrational spectroscopy of complexes of Al+ and Al2+ with ethane

   https://doi.org/10.1063/5.0266163  

   Ashraf, Muhammad Affawn; Metz, Ricardo B (April 2025, The Journal of Chemical Physics)

   The binding motifs of clusters of Al+ and Al2+ with ethane, Alx+(C2H6)n (x = 1, 2; n = 1–3), are determined using vibrational photodissociation spectroscopy in the C–H stretching region (2550–3100 cm−1) in conjunction with spectra calculated using density functional theory. The relative energies of candidate structures are determined with the B3LYP-D3 and ωB97X-D density functionals and the 6–311++G(d,p) basis set. Local mode Hamiltonian calculations are better able to reproduce the spectra than scaled harmonic calculations, due to contributions from bending overtones and combination bands. Vibrational photodissociation spectra show a red shift in the stretching frequencies of C–H bonds that are proximate to the cation. This red shift decreases as the number of ethanes increases. For Al+(C2H6)n (n = 1–3), side-on (T-shaped) binding of the metal is preferred to end-on binding, and subsequent ligands bind on the same side of the cation. Similarly, for Al2+(C2H6)n (n = 1–3), T-shaped configurations in which the C–C and Al–Al bonds are approximately perpendicular and the ethane binds side-on to the Al2+ are preferred. In Al2+(C2H6)n (n = 1–3) complexes, intense bands are observed, which are due to overtones and combinations of symmetric deformations in Fermi resonance with the red-shifted C–H stretches. 

   more » « less
5. Light-mediated aerobic oxidation of C(sp ³ )–H bonds by a Ce( iv ) hexachloride complex

   https://doi.org/10.1039/D2QO00362G  

   Wang, Yu-Heng; Yang, Qiaomu; Walsh, Patrick J.; Schelter, Eric J. (May 2022, Organic Chemistry Frontiers)

   A photochemical C(sp 3 )–H oxygenation of alkane and arene substrates catalyzed by [NEt 4 ] 2 [Ce IV Cl 6 ] under mild conditions (1 atm, 25 °C) is described. Time-course studies reveal that the hydrocarbons are oxidized in a stepwise fashion to afford alcohols, aldehydes, ketones, and carboxylic acids. The catalyst resting state, [Ce IV Cl 6 ] 2− , is observed by UV-visible spectroscopy. On/off light-switching experiments, quantum yield measurements, and the absence of a kinetic isotope effect on parallel C–H/C–D functionalization suggest that ligand-to-metal charge transfer of [NEt 4 ] 2 [Ce IV Cl 6 ] to generate Cl˙ is the turnover-limiting step. The involvement of a highly reducing excited-state [NEt 4 ] 3 [Ce III Cl 6 ]* species as well as photo-excited aldehyde, under black light irradiation appears to facilitate the conversion of primary alcohols and aldehydes to carboxylic acids. Remarkably, this approach is found to be capable of direct activation of light alkanes, including methane and ethane. 

   more » « less