Observation and assignment of silent and higher-order vibrations in the infrared transmission of C60 crystals

Analysis of Carbon Materials with Infrared Photoacoustic Spectroscopy

Measurement of infrared spectroscopy has emerged as a significant challenge for carbon materials due to the sampling problem. To overcome this issue, in this work, we performed measurements of IR spectra for carbon materials including C60, C70, diamond powders, graphene, and carbon nanotubes (CNTs) using the photoacoustic spectroscopy (PAS) technique; for comparison, the vibrational patterns of these materials were also studied with a conventional transmission method, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, or Raman spectroscopy. We found that the IR photoacoustic spectroscopy (IR-PAS) scheme worked successfully for these carbon materials, offering advantages in sampling. Interestingly, the profiles of IR-PAS spectra for graphene and CNTs exhibit negative bands using carbon black as the reference; the negative spectral information may provide valuable knowledge about the storage energy, production, structure, defect, or impurity of graphene and CNTs. Thus, this approach may open a new avenue for analyzing carbon materials.

Carbazole-functionalized cobalt(ii) porphyrin axially bonded with C60/C70 derivatives: synthesis and characterization

Depending on the structure of the fullero[60]/[70]pyrrolidine, the carbazole-functionalized cobalt(ii) porphyrin forms donor–acceptor systems of different compositions.

Matrix isolation spectroscopy and spectral simulations of isotopically substituted C60 molecules

Isotopically enriched (3.5% ¹³C) and depleted (0.5% ¹³C) fullerene C₆₀ molecules are isolated in parahydrogen (pH₂) solids at cryogenic temperatures and studied by high resolution (0.01-0.1 cm^-1) infrared (IR) absorption measurements. Spectra of natural isotopic abundance (1.1% ¹³C) C₆₀ molecules isolated in solid pH₂, orthodeuterium (oD₂), and Ne matrix hosts serve to identify the relatively minor spectral perturbations due to the trapping environments. Spectral features observed for the four IR-active T_1u modes of threefold degeneracy in I_h symmetry, namely, T_1u(1) at 529.77 cm^-1, T_1u(2) at 578.24 cm^-1, T_1u(3) at 1184.7 cm^-1, and T_1u(4) at 1432 cm^-1, are assigned to the superpositions of matrix perturbed vibrational-mode spectra of a number of ¹³C_n ¹²C_60-n isotopologues. New molecular orbital calculations show the symmetry lowering effects of ¹³C substitution, namely, split vibrational frequencies and modified IR intensities. IR spectral patterns calculated for the 328 distinct isotopomers of ¹³C_n ¹²C_60-n up to n = 3 are used to satisfactorily simulate most of the observed absorption features. For the T_1u(4) mode at 1432 cm^-1, the observed splitting is insensitive to the ¹³C abundance, indicating spectral perturbations due to Fermi resonance. Weak absorption features at 1545 cm^-1 are assigned to a combination of lower frequency modes. We discuss relative and absolute band strengths for the astrophysical application of estimating C₆₀ abundances in planetary nebulae.

Addition of tryptophan methyl-ester on [60]fullerene: theoretical investigation of the mechanisms of azomethine ylides and fulleropyrrolidine formation

In this paper, we perform the synthesization of carbon nanoparticles for active principle vectorization, with the suggestion of a reaction mechanism of tryptophan methyl ester addition on [60]fullerene. Firstly, we studied the effect of tryptophan form on its addition reaction on [60]fullerene. So, in order to determine the preferred environment that makes this reaction the most favorable, we considered all tryptophan possible forms in our investigation: the molecular, the zwitterionic, and the dibasic forms. Secondly, we investigate the proposed reaction mechanism of tryptophan methyl ester addition on [60]fullerene using theoretical thermodynamic calculation. Our hypothesis suggests the formation of azomethine ylide molecule in a first step followed by its addition on [60]fullerene in the second step by the photo-addition reaction involving the oxygen in its singlet state. The stability of each reactive intermediate involved in this mechanism is verified thermodynamically. The 12 most stable conformations of azomethine ylide were observed through potential energy surface analysis. They were obtained by a relaxed scan of the four dihedral angles. The calculations were conducted on the optimized geometry of fulleropyrrolidine mono-adduct and the bulk values of its thermodynamic constants were also determined. Infrared spectra observed in 100-4000 cm^-1 region confirmed our hypothesis suggesting the first step of azomethine ylide formation followed by the second step of azomethine ylide addition on [60]fullerene by ν(C_aliphatic-C-N), ν(C_aromatic-C-N) and ^δ(N-H) coupled with ν(C-N) absorption bond. Graphical abstract Optimized geometry of the Fulleropyrrolidine monoaduct molecule.

High-resolution photoelectron imaging of cold C₆₀⁻ anions and accurate determination of the electron affinity of C₆₀

High-resolution photoelectron imaging and spectroscopy of cold C₆₀⁻ anions are reported using a newly built photoelectron imaging apparatus coupled with an electrospray ionization source and a temperature-controlled cryogenic ion trap. Vibrationally resolved photoelectron spectra are obtained for the detachment transition from the ground state of C₆₀⁻ to that of C60 at various detachment wavelengths from 354.84 nm to 461.35 nm. The electron affinity of C60 is accurately measured to be 2.6835 ± 0.0006 eV. Numerous unexpected vibrational excitations are observed in the photoelectron spectra due to the Jahn-Teller effect in C₆₀⁻ and Hertzberg-Teller vibronic coupling in both C₆₀⁻ and C60. Both the relative intensities of vibrational peaks and their photoelectron angular distributions provide evidence for the vibronic couplings. The observed p-wave-like behavior in the angular distribution of the 0₀⁰ transition suggests that the electron is detached from an s-type orbital.

A complete nearest-neighbor force field model for C60

A force field model is developed for C(60) that features 13 force constants representing all interactions between nearest-neighboring atoms. The model is compared with, and tested against, other force field models in the literature. Force constants for C(60) are then deduced by fitting the model to the 14 known optically accessible vibrational frequencies of the molecule. Finally, the model is fitted to two existing theoretical calculations of the complete vibrational spectrum of C(60). Fair agreement is obtained with the theoretical calculations, implying that interactions with atoms other than nearest neighbors are small.