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Recently, some of us reviewed and studied the photoionization dynamics of C<sub>60</sub> that are of great interest to the astrochemical community as four of the diffuse interstellar bands (DIBs) have been assigned to electronic transitions in the C<sub>60</sub>$^+$ cation. Our previous analysis of the threshold photoelectron spectrum (TPES) of C<sub>60</sub> [Hrodmarsson et al., Phys. Chem. Chem. Phys. 22, 13880–13892 (2020)] appeared to give indication of D<sub>3d</sub>$^+$ ground state symmetry, in contrast to theoretical predictions of D<sub>5d</sub>$^+$ symmetry. Here, we revisit our original measurements taking account of a previous theoretical spectrum presented in the work of Manini et al., Phys. Rev. Lett. 91(19), 196402 (2003), obtained within a vibronic model parametrized on density functional theory/local-density approximation electronic structure involving all h<sub>g</sub> Jahn–Teller active modes, which couple to the $^2$H<sub>u</sub> components of the ground state of the C<sub>60</sub>$^+$ cation. By reanalyzing our measured TPES of the ground state of the C<sub>60</sub> Buckminsterfullerene, we find a striking resemblance to the theoretical spectrum calculated in the work of Manini et al., Phys. Rev. Lett. 91(19), 196402 (2003), and we provide assignments for many of the hg modes. In order to obtain deeper insights into the temperature effects and possible anharmonicity effects, we provide complementary modeling of the photoelectron spectrum via classical molecular dynamics (MD) involving density functional based tight binding (DFTB) computations of the electronic structure for both C<sub>60</sub> and C<sub>60</sub>$^+$. The validity of the DFTB modeling is first checked vs the IR spectra of both species which are well established from IR spectroscopic studies. To aid the interpretation of our measured TPES and the comparisons to the ab initio spectrum we showcase the complementarity of utilizing MD calculations to predict the PES evolution at high temperatures expected in our experiment. The comparison with the theoretical spectrum presented in the work of Manini et al., Phys. Rev. Lett. 91(19), 196402 (2003), furthermore, provides further evidence for a DC<sub>5d</sub> symmetric ground state of the C<sub>60</sub>$^+$ cation in the gas phase, in complement to IR spectroscopy in frozen noble gas matrices. This not only allows us to assign the first adiabatic ionization transition and thus determine the ionization energy of C<sub>60</sub> with greater accuracy than has been achieved at 7.598 ± 0.005 eV, but we also assign the two lowest excited states ($^2E$<sub>1u</sub> and $^2E$<sub>2u</sub>) which are visible in our TPES. Finally, we discuss the energetics of additional DIBs that could be assigned to C<sub>60</sub>$^+$ in the future.
This article corresponds to part II of a series about singly and multiply charged gold clusters. From their total energies in the size range n = 3 -20 and charge q = 0-4 determined in part I one of the series, it aims to present a Density Functional based Tight Binding approach of their stability/metastability versus atomization and fragmentation, as well as their ionization properties to different charge states. The present DFTB results are discussed with respect to previous theoretical or experimental investigations.
Mid-infrared emission features probe the properties of ionized gas, and hot or warm molecular gas. The Orion Bar is a frequently studied photodissociation region (PDR) containing large amounts of gas under these conditions, and was observed with the MIRI IFU aboard JWST as part of the "PDRs4All" program. The resulting IR spectroscopic images of high angular resolution (0.2") reveal a rich observational inventory of mid-IR emission lines, and spatially resolve the substructure of the PDR, with a mosaic cutting perpendicularly across the ionization front and three dissociation fronts. We extracted five spectra that represent the ionized, atomic, and molecular gas layers, and measured the most prominent gas emission lines. An initial analysis summarizes the physical conditions of the gas and the potential of these data. We identified around 100 lines, report an additional 18 lines that remain unidentified, and measured the line intensities and central wavelengths. The H I recombination lines originating from the ionized gas layer bordering the PDR, have intensity ratios that are well matched by emissivity coefficients from H recombination theory, but deviate up to 10% due contamination by He I lines. We report the observed emission lines of various ionization stages of Ne, P, S, Cl, Ar, Fe, and Ni, and show how certain line ratios vary between the five regions. We observe the pure-rotational H$_2$ lines in the vibrational ground state from 0-0 S(1) to 0-0 S(8), and in the first vibrationally excited state from 1-1 S(5) to 1-1 S(9). We derive H$_2$ excitation diagrams, and approximate the excitation with one thermal (~700 K) component representative of an average gas temperature, and one non-thermal component (~2700 K) probing the effect of UV pumping. We compare these results to an existing model for the Orion Bar PDR and highlight the differences with the observations.
This work examines the reliability of the Self Consistent Charge Density Functional based Tight Binding (SCC-DFTB) scheme to derive geometrical and thermochemistry observables for complexes and clusters made of Ag, C and H atoms. In addition to the currently available DFTB parameterization DFTBhyb, it proposes a new SCC-DFTB parameterization based on DFT Slater Koster integrals and recalibrated on atomic pairs MRCI calculations for clusters made of Ag, C and H atoms. Two sets of parameters were determined, one for restricted open shell SCC-DFTB, the other for spin-polarized SCC-DFTB. These two new sets of parameters, namely DFTB$^γ$ and DFTB$^{γpol}$ respectively, along with DFTB$^{hyb}$ , are first tested on Ag$_n$, Ag$_n$C and Ag$_n$H clusters. A key issue being the transferability of such parameters on different types of Ag-X bonds, the three sets of parameters are then tested on Ag$_m$C$_n$H$_p$ (m=1-3, n=2, p=0-2) complexes involving covalent and π metal-ligand bonds. The particular case of naphthalene C$_{10}$H$_8$ as a πligand is also investigated. In general, with respect to DFTB$^{hyb}$ results, using DFTB$^γ$ parameters leads to an improvement of geometries and energetics. In the case of Ag$_n$C$_{10}$H$_8$ clusters, the role of dispersion is evidenced. However, in a few cases, the geometries may distort due to a questionable description of charge transfer with DFTB$^γ$ and DFTB$^{γpol}$. The spin-polarized version of SCC-DFTB is suited to correctly describe open-shell species with more than one unpaired electron in their ground electronic state but is shown not to improve the results otherwise.
The radiative cooling of naphthalene dimer cations, (C$_{10}$H$_8$)$_2^+$ was studied experimentally through action spectroscopy using two different electrostatic ion-beam storage rings, DESIREE in Stockholm and Mini-Ring in Lyon. The spectral characteristics of the charge resonance (CR) band were observed to vary significantly with storage time of up to 30 seconds in DESIREE. In particular, the position of the CR band shifts to the blue, with specific times (inverse of rates) of 0.64 s and 8.0 s in the 0-5 s and 5-30 s storage time ranges, respectively. Such long-time scales evoke that the internal energy distribution of the stored ions evolves by vibrational radiative cooling, which is consistent with the absence of fast radiative cooling via recurrent fluorescence for (C$_{10}$H$_8$)$_2^+$. Density Functional based Tight Binding calculations with local excitations and Configuration Interactions (DFTB-EXCI) were used to simulate the absorption spectrum for ion temperatures between 10 and 500 K. The evolution of the band width and position with temperature is in qualitative agreement with the experimental findings. Furthermore, these calculations yielded linear temperature dependencies for both the shift and the broadening. Combining the relation between the CR band position and the ion temperature with the results of the statistical model, we demonstrate that the observed blue shift can be used to determine the radiative cooling rate of (C$_{10}$H$_8$)$_2^+$.
Sujets
CONSTANTS
BOMD
SCC-DFTB
Agrégats protonés
Alanine dipeptide
1
Modélisation
Clay mineral
Photon-dominated region PDR
Benzene
Charge resonance
Cryogenic ion trap
HAP
2
Agrégats protonés uracile-eau
Dehydrogenation mechanisms
Density functional tight binding
Atrazine
Benzene dimers
Electronic structure
Carbon clusters
Database
Barium
Configuration interaction
Amorphous
Atomic data
ADFT
Charge transfer state
Ammonium/ammonia water clusters
Threshold algorithm
CAH
Agrégats moléculaires
Molecular processes
Density functional theory
Anharmonic Infrared Spectroscopy
Line profiles
Argon
Molecular dynamics
Dynamique électronique
Dynamique moléculaire
CID
22 pole cryogenic ion trap
Charge
Agrégats aqueux
DFT
Collision Induced Dissociation
Chemical shift
Astrochimie
White dwarfs
Clustering
Auxiliary density functional theory
Water clusters
Agrégats d'eau
Molecular data
Molecular clusters
Quantum chemistry
DFTB
Agrégats aqueux d'ammonium/ammoniac
Probability flows
Nanoparticles
DFTB-CI
Atomic scattering from surfaces
Catalyse
Brown dwarfs
CONFIGURATION-INTERACTION
Astrochemistry
Agrégats
Charged system and open shell
Approche mixte quantique/classique
Excited states
Abundances -ISM
Car-Parrinello molecular dynamics
Corannulene
Biodegradation
Infrared spectra
ISM molecules
Polycyclic aromatic hydrocarbon PAH
Argile
Density Functional Theory
Gold clusters
PAH
Infrared ISM
Carbon cluster
Polycyclic aromatic hydrocarbons
Modelling
Polycyclic Aromatic Hydrocarbons
Clusters
Carbonaceous grains
Density functional based tight binding DFTB
Chimie quantique
Au147
Champ de forces
DUST
Disconnectivity tree
Methods laboratory molecular
Optical spectra
QSAR
Infrared spectroscopy
Catalysis