Infrared spectroscopy of ionized corannulene in the gas phase

Abstract

The gas-phase infrared spectra of radical cationic and protonated corannulene were recorded by infrared multiple-photon dissociation (IRMPD) spectroscopy using the IR free electron laser for infrared experiments. Electrospray ionization was used to generate protonated corannulene and an IRMPD spectrum was recorded in a Fourier-transform ion cyclotron resonance mass spectrometer monitoring H-loss as a function of IR frequency. The radical cation was produced by 193-nm UV photoionization of the vapor of corannulene in a 3D quadrupole trap and IR irradiation produces H, H 2 , and C 2 H x losses. Summing the spectral response of the three fragmentation channels yields the IRMPD spectrum of the radical cation. The spectra were analyzed with the aid of quantum-chemical calculations carried out at various levels of theory. The good agreement of theoretical and experimental spectra for protonated corannulene indicates that protonation occurs on one of the peripheral C-atoms, forming an sp 3 hybridized carbon. The spectrum of the radical cation was examined taking into account distortions of the C 5v geometry induced by the Jahn-Teller effect as a consequence of the degenerate 2 E 1 ground electronic state. As indicated by the calculations, the five equivalent C s minima are separated by marginal barriers, giving rise to a dynamically distorted system. Although in general the character of the various computed vibrational bands appears to be in order, only a qualitative match to the experimental spectrum is found. Along with a general redshift of the calculated frequencies, the IR intensities of modes in the 1000-1250 cm −1 region show the largest discrepancy with the harmonic predictions. In addition to CH "in-plane" bending vibrations, these modes also exhibit substantial deformation of the pentagonal inner ring, which may relate directly to the vibronic interaction in the radical cation.

The infrared spectra of nonplanar polycyclic aromatic hydrocarbons with five- or seven-membered rings

“…In such cases dynamic Jahn-Teller effects could be important. However, as discussed previously [8,23,22,24], theory using the harmonic approximation and experiment are in good agreement even in those cases where there is a Jahn-Teller distortion. The Jahn-Teller active modes can have a somewhat larger error, but it is still sufficiently small to assign the modes.…”

Interstellar C60+

“…This combination is known to yield reasonably accurate vibrational frequencies, after scaling with an empirical factor χ to account for the overestimation of the frequencies. The relatively small basis set limits the accuracy of band intensities, but based on the thorough tests performed by Galué et al (2011), we expect that neglecting dynamical JT effects is the leading limitation on vibrational band accuracy even at this level of theory. The distorted geometry of minimum energy was obtained by optimizing with no symmetry constraints, and turned out to have D 5v symmetry.…”

“…A comparable, but much simpler case of dynamical JT effect is the cation of corannulene, C 20 H + 10 , which can be regarded as a fragment of C 60 with peripheral bonds saturated by H atoms. This was studied by Galué et al (2011), who compared experimental infrared, multiphoton dissociation (IRMPD) spectra with a plain DFT harmonic vibrational analysis at the distorted geometry of minimum energy. This was expected to be the worst possible comparison, since in IRMPD experiments, vibrational energy is increased until the dissociation threshold is reached.…”

Theoretical study of the corannulene ozonolysis and evaluation of the various reaction paths

“…1) [9]. It is a highly symmetric molecule (C 5 V) belonging to the family of the polycyclic aromatic hydrocarbons [10,11]. One of the most promising materials in nanotechnology is graphene that is a limiting zerocurvature case.…”