Electron-phonon coupling and vibrational properties of size-selected linear carbon chains by resonance Raman scattering

Abstract

UV resonance Raman spectroscopy of size-selected linear sp-carbon chains unveils vibrational overtones and combinations up to the fifth order. Thanks to the tunability of the synchrotron source, we excited each H-terminated polyyne (HCnH with n = 8,10,12) to the maxima of its vibronic absorption spectrum allowing us to precisely determine the electronic and vibrational structure of the ground and excited states for the main observed vibrational mode. Selected transitions are shown to enhance specific overtone orders in the Raman spectrum in a specific way that can be explained by a simple analytical model based on Albrecht’s theory of resonance Raman scattering. The determined Huang–Rhys factors indicate a strong and size-dependent electron-phonon coupling increasing with the sp-carbon chain length.

Size dependence of optical nonlinearity for H-capped carbon chains, H–(CC)n–H (n = 3–15): analysis of its nature and prediction for long chains

“…It is worth mentioning that our previous study on the optical nonlinearities of cyclo[2N]carbon (N = [3][4][5][6][7][8][9][10][11][12][13][14][15] shows that the size dependence of (hyper)polarizability follows different rules according to the parity of N in cyclic carbon molecules, 34 while the change characteristics of carbon chains H-(CRC) n -H (n = 3-15) with odd and even C-C units are consistent. Compared with the cyclo[2N]carbon (N = 3-15), H-capped carbon chains with the same number of carbons show significant response properties a iso (l) and g 8 (l) (l = N, 1907, 1460, 1340, and 1064 nm).…”

“…[4][5][6] Alternatively, the polyynes with a generic formula of R 1 -(CRC) n -R 2 were used as a model for carbon chains to predict their properties. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] Polymers H-(CRC) n -H, i.e., H-capped carbon chains, are perhaps the simplest and yet most intriguing species of them.…”

High‐Density Atomic Fe–N4/C in Tubular, Biomass‐Derived, Nitrogen‐Rich Porous Carbon as Air‐Electrodes for Flexible Zn–Air Batteries

“…The decreasing ratio between D and G band ( I D / I G ) in the Raman spectra indicates the higher degree of graphitization with transition‐metals doping (Figure 2g). [ 26 ] The X‐ray photoelectron spectroscopy (XPS) measurements are conducted to demonstrate the electronic structure of different elements on surfaces of the as‐prepared samples (Figure S7, Supporting Information). Based on the deconvolution results of N 1 s spectrums, the sample (CZ) directly derived from CS exhibits a high nitrogen content ≈5 wt.%.…”

Impact of Halogen Termination and Chain Length on π-Electron Conjugation and Vibrational Properties of Halogen-Terminated Polyynes

“…Among the most assessed characterization techniques, UV–vis absorption spectra of these systems present a sequence of vibronic peaks whose position is strictly dependent on their length and their terminations. ,,− Raman spectra of polyynes present a very characteristic mode called effective conjugation coordinate (or α) (i.e., ECC), which consists of a collective vibration of all of the CC bonds of the sp-chain. The ECC mode fits in a frequency region (1800–2300 cm –1 ) where all the other carbon nanostructures do not have any Raman-active mode, thus making the ECC band a perfect marker to detect the presence of sp-hybridized carbon structures. ,− The frequency of the ECC band shifts with the structure of the chains, providing information on the length, terminations, π-electron conjugation, and electron–phonon coupling. ,,, In centrosymmetric linear sp-carbon wires, the ECC mode does not induce a variation in the molecular dipole moment and is not IR active. Nevertheless, the ECC mode becomes IR active for heteroterminations or deviations from chain linearity breaking the inversion symmetry. − …”