Time-resolved EPR and Fourier transform EPR study of triplet fullerene C60: determinations of T1 and the carbon-13 hyperfine coupling constant (original) (raw)
Related papers
The Journal of Physical Chemistry, 1993
Continuous wave (CW) and time-resolved (TR) EPR spectra of triplet Cao with partial and full 13C enrichment in methylcyclohexane solutions after UV irradiation were obtained. Line broadening from 1% satellites was observed. The I3C hyperfine coupling constant was determined to be 0.06 G. Fourier transform EPR (FT-EPR) experiments with a resolution of 20 ns were carried out, and T I was found to be 0.8 f 0.1 p s by fitting the intensity of the free induction decay signal to the modified Bloch equations. The relaxation time from Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, under Contract W-3 1-109-Eng-38. The work at The University of Chicago was supported by NSF Grant CHE-9021-487. DuPont Contribution No. 6472. We thankDr. M. Bowman for help in the FT-EPR experiments, Jerry Hunt for mass spectroscopy assistance, and Steve Hill for technical support in the CW-EPR experiments.
A theoretical investigation of four electronic states of C6− and the ground state of linear C6
Chemical Physics Letters, 1995
Large-scale open-shell coupled cluster calculations have been carried out for the four lowest doublet states of C~ and the ground state of linear C 6. They strongly support the assignment of the peaks at 607.7 and 586.5 nm observed in neon matrix isolation experiments to the 0 ° and 31 transitions within the electronic band (~ 2IIg ~-X 21-Iu of C~. The vibrational structure of the photoelectron spectrum of C~ has been calculated; the 15 transition is calculated to have 42% intensity with respect to the adiabatic peak. Some misassignments of the experimental threshold photodetachment and autodetachment spectra are corrected. Excellent agreement with experiment is obtained for the electron affinity of linear C 6.
Spectroscopic Survey of Electronic Transitions of C6H, (13)C6H, and C6D
The journal of physical chemistry. A, 2016
Electronic spectra of C 6 H are measured in the 18 950´21 100 cm´1 domain using cavity ring-down spectroscopy of a supersonically expanding hydrocarbon plasma. In total, 19 (sub)bands of C 6 H are presented, all probing the vibrational manifold of the B 2 Π electronically excited state. The assignments are guided by electronic spectra available from matrix isolation work, isotopic substitution experiments (yielding also spectra for 13 C 6 H and C 6 D), predictions from ab initio calculations as well as rotational fitting and vibrational contour simulations using the available ground state parameters as obtained from microwave experiments. Besides the 0 0 0 origin band, three non-degenerate stretching vibrations along the linear backbone of the C 6 H molecule are assigned: the ν 6 mode associated with the CC bond vibration and the ν 4 and ν 3 modes associated with C"C triple bonds. For the two lowest ν 11 and ν 10 bending modes, a Renner-Teller analysis is performed identifying the µ 2 Σ(ν 11) and both µ 2 Σ(ν 10) and κ 2 Σ(ν 10) components. In addition, two higher lying bending modes are observed, which are tentatively assigned as µ 2 Σ(ν 9) and µ 2 Σ(ν 8) levels. In the excitation region below the first non-degenerate vibration (ν 6), some 2 Π´2Π transitions are observed that are assigned as even combination modes of low-lying bending vibrations. The same holds for a 2 Π´2Π transition found above the ν 6 level. From these spectroscopic data and the vibronic analysis a comprehensive energy level diagram for the B 2 Π state of C 6 H is derived and presented.
Electronic Excitations and Stability of the Ground State of C60 Molecules
1998
A model study of the singlet excitons in the C60 molecule with emphasis on the Coulomb interaction between excited electron and hole leads to a physical understanding of the interaction effects on the absorption spectra and to a new identification of the forbidden excitons in the third-harmonic generation spectra. These conclusions may be tested experimentally on the model predictions related to the optical Kerr effect. The model shows that, with sufficiently strong interatomic than onsite interaction, a T_{2G} exciton could have very low energy or become unstable against the closed-shell ground state. Properties of these interesting cases beyond the C60 are briefly examined.
Electronic transition of C 3 H − in the vicinity of the lowest photodetachment threshold
Molecular Physics, 2001
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Journal of Physical Chemistry A, 2002
Carbon molecules were produced by evaporation of graphite and matrix-isolated in solid neon and argon. Using synchrotron radiation, the absorption spectra of the carbon clusters were recorded from 1100 to 5600 Å, and the fluorescence or phosphorescence spectra were recorded from 1200 to 9000 Å. We observed an intense, broad absorption band system centered at around 1600 Å in neon and 1700 Å in argon. By measuring the excitation spectrum of the a 3 Π u f X 1 Σ + g phosphorescence and checking the intensity correlation with the known 1 Π u r X 1 Σ + g absorption band, we could show that the observed VUV band system is the allowed 1 Σ + u r X 1 Σ + g electronic transition of the C 3 molecule. At the blue and the red side of the band system, distinct progressions can be observed which most likely correspond to a symmetric stretch of about ν 1 ≈ 1100 cm -1 and a bending mode of about ν 3 ≈ 550 cm -1 , respectively. In the band center, however, a complicated superposition of several vibrational progressions appears indicating that besides the 1 Σ + u state also other states seem to contribute to the absorption. Quantum chemical MR-AQCC calculations suggest that these contributing states are 1 Π g states which are close in energy to the 1 Σ + u state and can interact via vibronic coupling, a conjecture supported by preliminary calculations of synthetic spectra in which such coupling was included. Furthermore, the calculations show that the 1 Σ + u energy decreases upon bending, leading to a complex landscape of energy surfaces which include avoided crossing type features, and rendering more detailed spectral calculations difficult.
Structure and electronic spectra of the C anion
Monthly Notices of the Royal Astronomical Society, 2012
Ab initio calculations are employed for determining structures, spectroscopic parameters and transitions to the excited electronic states of the astrophysical relevant C − 6 anion, which is a potential intermediate of chemical processes involving carbon chains and polycyclic aromatic hydrocarbons. Calculations confirm the prominent stability of linear carbon chain anions which guarantees their formation. The lowest doublet potential energy surface of C − 6 displays six isomers, whereas in the lowest quartet potential energy surface, a unique minimum energy geometry is found. The most stable form is the linear anion l-C − 6 (X 2 u) followed by the cC − 6 (X 2 A 1 ') at 9291 cm −1 above in energy, which presents a distorted D 3h structure. The other isomers are also located at more than 9000 cm −1 above l-C − 6 (X 2 u). For each isomer, a set of spectroscopic parameters including their equilibrium structures, rotational constants at equilibrium, harmonic wavenumbers, dipole moments and electron affinities are predicted. For linear C − 6 , eight electronic states lying below the electron detachment threshold, are computed. Four doublet electronic states, which play important roles in the C − 6 reactivity, lie below 2 eV. Spin-orbit constants for the upper electronic states of l-C − 6 are predicted.
Electronic excitations in fullerenes: Jahn-Teller distorted structures of C60
Journal of Molecular Structure, 1994
The ground state wavefunction of the neutral icosahedral C 60 molecule belongs to the total symmetric one-dimensional A g representation. However, the degeneracy of the HOMO is five-fold while the LUMO is triply degenerate. This means that the lowest excited and ionized many-electron states will also be degenerate, and thus they are subjected to Jahn-Teller distortions. In this work we used a simple model Hamiltonian to study the extent and energy of the distortions arising due to excitations. For the -r-electrons we used a Pariser-Parr-Pople type wavefunction augmented by an empirical potential to describe the (J cores. The zr-electron part of the Hamiltonian depends on the bond lengths which can be optimized by means of simple gradient techniques. The excited states are described by the Tamm -Dancoff approximation (all single CI). In order to locate the distorted states on the energy hypersurface, the degenerate excited states were reduced according to those subgroups of the I h group that contain one-dimensional (that is, Jahn--Teller inactive) irreducible representations in an excitation subspace. Distorted structures of D 2h , D 3d , D Sd and T h symmetries were determined. The extent of the distortions is small, the largest change in bond lengths being 0.02 A. The Jahn Teller distortion energies were found to be typically I~3 kcal mol": Singlet and triplet excited state spectra were computed using the CNDO/S-CI method. Comparison of the calculated spectra with experimental results shows evidence of JahnT eller distortions.
Optics and Spectroscopy, 2005
The singlet-singlet and triplet-triplet absorption spectra of C 60 fullerene are calculated using the density functional method and taking into account the theory of linear and quadratic responses. The B3LYP density functional and the 6-31G and 3-21G atomic basis sets are used. The calculations are performed using the D 2 h and D 5 d symmetry groups, although the real symmetry of the ground state is described by the I h symmetry group. The matrix elements of the operator of the spin-orbit coupling are calculated and the probabilities of some singlet-triplet transitions are estimated. Taking into account the data in the literature on vibronic interactions of vibrations of the t 1 u , t 2 u , g u , and h u symmetry species, the radiative lifetime of the 1 3 T 2 g 1 1 A g phosphorescence was estimated to be 45 s. The fact that this time proved to be considerably greater than the experimentally observed total lifetime of the triplet testifies to a fast nonradiative deactivation of the lowest triplet state of C 60 fullerene and agrees with a low phosphorescence intensity. The zero-field splitting of some triplets and the intensities of magnetic dipole transitions are discussed.
Vibrational relaxation dynamics of the X̃1∑g+ state of C3
Chemical Physics Letters, 1982
The vrbrational relaxauon dynamics of the ground '$ electronic start oiCJ has been studied iollo~rng IR mulrrple photon diiociatron of aknc. Wavelength and trmc resolved spectra, using dye laser-Induced ~luorcsccncc arc used to charactetue the vibrational levels and Iheir CorKspondfflP nse and decay rates. \'rbratronal rclaxrlion rates arc rcportcd for+ C3(' $. 100 or 1 IO) in the presence of Ar. He, Nz. 0:. and CzHz, rn addrtron to the reactron raw constant of C~('~,.@OO) nirh CzH2 of(Z.2 f 0 10) X ICI-" cm3 molecule-' s-'.