More Like this

1. Adiabatic ionization energies of RuC, RhC, OsC, IrC, and PtC

   https://doi.org/10.1063/5.0194848  

   Merriles, Dakota M. ; Barrera-Casas, Yexalen ; Knapp, Annie S. ; Morse, Michael D. ( February 2024 , The Journal of Chemical Physics)

   The ionization energies (IEs) of RuC, RhC, OsC, IrC, and PtC are assigned by the measurement of their two-photon ionization thresholds. Although late transition metal–carbon bonds are of major importance in organometallic chemistry and catalysis, accurate and precise fundamental thermochemical data on these chemical bonds are mainly lacking in the literature. Based on their two-photon ionization thresholds, in this work, we assign IE(RuC) = 7.439(40) eV, IE(RhC) = 7.458(32) eV, IE(OsC) = 8.647(25) eV, IE(IrC) = 8.933(74) eV, and IE(PtC) = 9.397(32) eV. These experimentally derived IEs are further confirmed through quantum chemical calculations using coupled-cluster single double perturbative triple methods that are extrapolated to the complete basis set limit using a three-parameter mixed Gaussian/exponential extrapolation scheme and corrected for spin–orbit effects using a semiempirical method. The electronic structure and chemical bonding of these MC species are discussed in the context of these ionization energy measurements. The IEs of RuC, RhC, OsC, and IrC closely mirror the IEs of the corresponding transition metal atoms, suggesting that for these species, the (n + 1)s electrons of the transition metals are not significantly involved in chemical bonding.

    

   more » « less
2. Bond dissociation energies of diatomic transition metal nitrides

   https://doi.org/10.1063/5.0141182  

   Merriles, Dakota M. ; Knapp, Annie S. ; Barrera-Casas, Yexalen ; Sevy, Andrew ; Sorensen, Jason J. ; Morse, Michael D. ( February 2023 , The Journal of Chemical Physics)

   Resonant two-photon ionization (R2PI) spectroscopy has been used to measure the bond dissociation energies (BDEs) of the diatomic transition metal nitrides ScN, TiN, YN, MoN, RuN, RhN, HfN, OsN, and IrN. Of these, the BDEs of only TiN and HfN had been previously measured. Due to the many ways electrons can be distributed among the d orbitals, these molecules possess an extremely high density of electronic states near the ground separated atom limit. Spin–orbit and nonadiabatic interactions couple these states quite effectively, so that the molecules readily find a path to dissociation when excited above the ground separated atom limit. The result is a sharp drop in ion signal in the R2PI spectrum when the molecule is excited above this limit, allowing the BDE to be readily measured. Using this method, the values D0(ScN) = 3.905(29) eV, D0(TiN) = 5.000(19) eV, D0(YN) = 4.125(24) eV, D0(MoN) = 5.220(4) eV, D0(RuN) = 4.905(3) eV, D0(RhN) = 3.659(32) eV, D0(HfN) = 5.374(4) eV, D0(OsN) = 5.732(3) eV, and D0(IrN) = 5.115(4) eV are obtained. To support the experimental findings, ab initio coupled-cluster calculations extrapolated to the complete basis set limit (CBS) were performed. With a semiempirical correction for spin–orbit effects, these coupled-cluster single double triple-CBS calculations give a mean absolute deviation from the experimental BDE values of 0.20 eV. A discussion of the periodic trends, summaries of previous work, and comparisons to isoelectronic species is also provided.

    

   more » « less
3. High-level ab initio composites: thermochemical bond dissociation energies for vanadium species

   https://doi.org/10.1080/00268976.2023.2248292  

   Welch, Bradley ; McLean, Ryan ; Wilson, Angela K. ( December 2023 , Molecular Physics)

   Bond dissociation energies (BDE) are key descriptors for molecules and are among the most sought-after properties in chemistry. Despite their importance, the accurate prediction of BDE’s for transition metal species can be particularly daunting for both experiment and computation. Experimental data has been limited and, when available, often has large error bars, making the critical evaluation and identification of suitable computational methods difficult. However, recent advancements in the experimental determination of BDE’s with techniques such as Velocity Map Imaging and 2 Photon Ionization now provide useful gauges for computational strategies and new methodologies, providing energies with unprecedented accuracies. The vanadium diatomics (VX, X=B, C, N, O, F, Al, Si, P, S, Cl) have been challenging for computational chemistry methods, and, thus, a new experimental gauge enables methods to be reevaluated and developed for these species. Herein, the super-correlation consistent Composite (super-ccCA or s-ccCA), a new thermochemical scheme centered around CCSD(T)/complete basis set (CBS) limit computations with additional contributions that account for scalar-relativistic effects, and coupled cluster contributions beyond CCSD(T) up to quintuple excitations has been considered. The agreement between determinations made by the s-ccCA scheme and by recent experiment is excellent, demonstrating the utility of the new approach in addressing challenging metal systems, even those of multireference nature. In light of recent experimental BDE’s, the longstanding correlation consistent composite approach (ccCA) is also evaluated for the VX species and find that the mean absolute deviation (MAD) is greatly reduced compared to previously used experimental values. 

   more » « less
4. Benchmark PhotoIonization Cross-Sections of Neutral Scandium from the Ground and Excited States

   https://doi.org/10.3390/atoms9040083  

   Tayal, Swaraj S. ; Zatsarinny, Oleg ( December 2021 , Atoms)

   The B-spline R-matrix method has been used to investigate cross-sections for photoionization of neutral scandium from the ground and excited states in the energy region from the 3d and 4s valence electron ionization thresholds to 25 eV. The initial bound states of Sc and the final residual Sc+ ionic states have been accurately calculated by combining the multiconfiguration Hartree-Fock method with the frozen-core close-coupling approach. The lowest 20 bound states of Sc I belonging to the ground 3d4s2 and excited 3d24s, 3d24p, 3d4s4p, 4s24p, and 3d3 configurations have been considered as initial states. The 81 LS final ionic states of Sc+ belonging to the terms of 3p63d2, 3p63d4l (l = 0–3), 3p63d5l (l = 0–3), 3p63d6s, 3p64s2, 3p64s4l (l = 0–3), 3p64s5l (l = 0–1), and 3p64p2 configurations have been included in the final-state close-coupling expansion. The cross-sections are dominated by complicated resonance structures in the low energy region converging to several Sc+ ionic thresholds. The inclusion of all these final ionic states has been noted to significantly impact the near-threshold resonance structures and background cross-sections. The important scattering channels for leaving the residual ion in various final states have been identified, and the 3d electron ionization channels have been noted to dominate the cross-sections at higher photon energies. 

   more » « less
5. On the formation and the isomer specific detection of methylacetylene (CH 3 CCH), propene (CH 3 CHCH 2 ), cyclopropane (c-C 3 H 6 ), vinylacetylene (CH 2 CHCCH), and 1,3-butadiene (CH 2 CHCHCH 2 ) from interstellar methane ice analogues

   https://doi.org/10.1039/C8CP03921F  

   Abplanalp, Matthew J. ; Góbi, Sándor ; Kaiser, Ralf I. ( March 2019 , Physical Chemistry Chemical Physics)

   Pure methane (CH 4 ) ices processed by energetic electrons under ultra-high vacuum conditions to simulate secondary electrons formed via galactic cosmic rays (GCRs) penetrating interstellar ice mantles have been shown to produce an array of complex hydrocarbons with the general formulae: C n H 2n+2 ( n = 4–8), C n H 2n ( n = 3–9), C n H 2n−2 ( n = 3–9), C n H 2n−4 ( n = 4–9), and C n H 2n−6 ( n = 6–7). By monitoring the in situ chemical evolution of the ice combined with temperature programmed desorption (TPD) studies and tunable single photon ionization coupled to a reflectron time-of-flight mass spectrometer, specific isomers of C 3 H 4 , C 3 H 6 , C 4 H 4 , and C 4 H 6 were probed. These experiments confirmed the synthesis of methylacetylene (CH 3 CCH), propene (CH 3 CHCH 2 ), cyclopropane (c-C 3 H 6 ), vinylacetylene (CH 2 CHCCH), 1-butyne (HCCC 2 H 5 ), 2-butyne (CH 3 CCCH 3 ), 1,2-butadiene (H 2 CCCH(CH 3 )), and 1,3-butadiene (CH 2 CHCHCH 2 ) with yields of 2.17 ± 0.95 × 10 −4 , 3.7 ± 1.5 × 10 −3 , 1.23 ± 0.77 × 10 −4 , 1.28 ± 0.65 × 10 −4 , 4.01 ± 1.98 × 10 −5 , 1.97 ± 0.98 × 10 −4 , 1.90 ± 0.84 × 10 −5 , and 1.41 ± 0.72 × 10 −4 molecules eV −1 , respectively. Mechanistic studies exploring the formation routes of methylacetylene, propene, and vinylacetylene were also conducted, and revealed the additional formation of the 1,2,3-butatriene isomer. Several of the above isomers, methylacetylene, propene, vinylacetylene, and 1,3-butadiene, have repeatedly been shown to be important precursors in the formation of polycyclic aromatic hydrocarbons (PAHs), but until now their interstellar synthesis has remained elusive. 

   more » « less