Disentangling Electronic Spectra of Linear and Cyclic Hydrogenated Carbon Cluster Cations, C_2n+1H⁺ (n = 3–10)

Abstract

Electronic spectra are measured for protonated carbon clusters (C2n+1H+) containing between 7 and 21 carbon atoms. Linear and cyclic C2n+1H+ isomers are separated and selected using a drift tube ion mobility stage before being mass selected and introduced into a cryogenically cooled ion trap. Spectra are measured using a two-color resonance-enhanced photodissociation strategy, monitoring C2n+1 + photofragments (H atom loss channel) as a function of excitation wavelength. The linear C7H+, C9H+, C11H+, C13H+, C15H+, and C17H+ clusters, which are predicted to have polyynic structures, possess sharp 11Σ+ ← X̃1Σ+ transitions with well-resolved vibronic progressions in C–C stretch vibrational modes. The vibronic features are reproduced by spectral simulations based on vibrational frequencies and geometries calculated with time-dependent density functional theory (ωB97X-D/cc-pVDZ level). The cyclic C15H+, C17H+, C19H+, and C21H+ clusters exhibit weak, broad transitions at a shorter wavelength compared to their linear counterparts. Wavelengths for the origin transitions of both linear and cyclic isomers shift linearly with the number of constituent carbon atoms, indicating that in both cases, the clusters possess a common structural motif.

Probing Colossal Carbon Rings

“…To address this issue, we have developed an isomer selective approach for measuring electronic spectra. 24,26,34 The experimental arrangement is shown schematically in Figure 1(c) and is described in more detail in refs 24 and 26.…”

“…Obtaining electronic or infrared spectra of larger cyclo­[ n ]carbon cations entails dealing with complications associated with the presence of different isomers (rings, bi-rings and fullerenes), whose spectra may be entangled. To address this issue, we have developed an isomer selective approach for measuring electronic spectra. ,, The experimental arrangement is shown schematically in Figure (c) and is described in more detail in refs and .…”

Virtual Issue on Photodissociation: From Fundamental Dynamics and Spectroscopy to Photochemistry in Planetary Atmospheres and in Space

“…This method of photodissociation or photodepletion (PD) spectroscopy has found numerous uses. An important application is the study of structures and spectra (both vibrational and electronic) of charged clusters 5,34 and organic chromophores, the latter for comparison with spectra in solution or in photoactive proteins. 30,31 In addition, the approach has been used to investigate competition between ion fragmentation pathways; 22 microsolvation of metal ions by ligands such as water or organic molecules (with control of the number of ligands by initial mass selection of the cluster); 33 proton transfer in protonated clusters of organic or biological molecules with water; 32 host−guest supramolecular complexes; 6 and the structures and wavelength-dependent absorption cross sections of semiconductor nanoparticles.…”

“…Small molecular clusters held together by weak, noncovalent interactions can be prepared in the low temperature environment of a molecular beam, and their photodissociation dynamics can be studied using the same methods developed for isolated molecules. ,, Other strategies to produce clusters of various types include electrospray of anions or cations, ,,, plasma expansion, or laser ablation from a metal or graphite target. ,, Charged clusters can be accumulated, stored, and cooled in ion traps, entrained in supersonic expansions, or separated by ion mobility through a buffer gas. Microsolvation in these clusters offers a bridge between photodissociation in the gas phase and in solution, allowing in-depth study of the impacts of intermolecular interactions on photochemical outcomes.…”

“…7,12,13 Other strategies to produce clusters of various types include electrospray of anions or cations, 6,22,30,31 plasma expansion, 32 or laser ablation from a metal or graphite target. 5,33,34 Charged clusters can be accumulated, stored, and cooled in ion traps, entrained in supersonic expansions, or separated by ion mobility through a buffer gas. Microsolvation in these clusters offers a bridge between photodissociation in the gas phase and in solution, allowing in-depth study of the impacts of intermolecular interactions on photochemical outcomes.…”