Electron Nuclear Double Resonance in Photoexcited Triplet-State Benzene-<i>h</i>6 Molecules in Benzene-<i>d</i>6 Single Crystals

Goncalves, A. M. Ponte; Hutchison, Clyde A.

doi:10.1063/1.1670747

Cited by 60 publications

(8 citation statements)

References 7 publications

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“…In the next few years the triplet state of benzene C 6H6 in a C6D6 crystalline host was thoroughly studied by electron nuclear double resonance (ENDOR) [17], EPR [18] and phosphorescence excitation spectroscopy [19]. The results lent strong support to Moffitt and Liehr 's general ideas about what might happen when benzene is excited.…”

Section: Conformational Instability ("Jahn-teller Effect')supporting

confidence: 57%

EPR of photo-excited triplet states: A personal account

Waals

2001

Appl. Magn. Reson.

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A sketch is presented of the path that has led from Zavoisky's pioneering experiments to modern investigations by electron paramagnetic resonance (EPR) of the phosphorescent (S = 1) triplet state of polyatomic molecules or ions. The group-theoretical method first introduced by Wigner in his analysis of the multiplets of atomic spectroscopy, likewise provides a key for understanding the zero-field splitting and selection rules for radiative decay of the phosphorescent triplet state. Examples to illustrate the progress made through EPR experiments are selected from three fields. (i) Conformational instability on excitation. Both the zero-field splitting and the electron spin density distribution provide unique fingerprints of a triplet state's geometry -structural information of a kind that is nonexistent for singlet states! Illustrations are provided by benzene C 6 H6 and fullerene C60 . (ii) The optical pumping cycle. The spin selectivity of singlet-to-triplet intersystem crossing and radiative decay of the individual spin components of the triplet state is discussed. In practice this selectivity is put to advantage by performing EPR on triplet states in zero-field by means of optical detection. In turn, such experiments have led to a detailed insight into the spin-orbit coupling mechanisms responsible for the spin selectivity of the above processes. The high sensitivity attainable with optical detection has recently culminated in EPR experiments on single molecules. (iii) Quantum interference. In a triplet state of low symmetry two of the spin sublevels may decay to the ground state by the emission of photons of a common polarization (i.e., out of plane for an aromatic hydrocarbon). In such a situation quantum interference between the two decay channels can be induced by an appropriate preparation of the excited state. An example is shown where flash-excitation in the singlet manifold followed by rapid intersystem crossing causes the S = 1 spin angular momentum to be created in a spin state which is not an eigenstate of the zero-field splitting tensor. This nonstationary character of the initial triplet state, which reflects the spin-orbit coupling pathway, is observed through the detection of a spontaneous microwave signal following the 25 ps laser flash.

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Section: Conformational Instability ("Jahn-teller Effect')supporting

confidence: 57%

EPR of photo-excited triplet states: A personal account

Waals

2001

Appl. Magn. Reson.

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“…The experimental observation that in the benzene crystal one of the in-plane zero-field axes falls along a molecular diagonal [12,13] appears a surprising coincidence in the present model, Perhaps it is an indication that the ' hexagonal' coupling is more important than hitherto assumed. Because intuitively one would expect that the stronger this coupling, the more the molecular conformation in a crystalline environment will tend to one of the three minima in the BornOppenheimer potential.…”

Section: Io/i•176mentioning

confidence: 54%

“…Ponte Goncalves and Hutchison from their ENDOR studies further concluded that there are three distinct pairs of protons (in agreement with the inversion symmetry in the crystal), with the 1,4 pair having a substantially lower isotropic ENDOR shift than the two other, nearly equal pairs; also the molecule was found to be non-planar [13]. Partly because of this non-planarity, complications arise in the determination of the spin distribution; using two different methods Ponte Goncalves and Hutchison find pl/(p2~ p3)=0"87 or 0.83, i.e.…”

Section: Experiments In Relation To Theorymentioning

confidence: 61%

“…On the other hand, a weak crystal field which produces only minor changes in the vibronic energies, may still cause the marked departures from hexagonal symmetry of the electron spin distribution observed in magnetic resonance experiments [11][12][13] on the benzene crystal and may also explain the characteristic splitting observed for the strongest band of the To+-So absorption spectrum [10].…”

Section: --'Eumentioning

confidence: 99%

See 1 more Smart Citation

Vibronic interaction in the lower electronic states of benzene

Waals¹,

Berghuis

Groot

1971

Molecular Physics

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Results of further calculations on the dynamic coupling between the lower Blu and Elu electronic states of benzene via a single e2g mode are presented. In part I we gave the 'pseudo-cylindrical' solutions that result when the leading coupling term, linear in the nuclear displacements, is considered (cylindrical Born-Oppenheimer potential). Here we investigate the effect of (1) the next higher terms in the expansion of the coupling hamiltonian for the free molecule (hexagonal Born-Oppenheimer potential); (2) a crystal field anisotropy. From the scanty data on the coupling constants available a priori it would follow that the refinement introduced by (1) is small for benzene. On the contrary, the effect of even a small crystal field anisotropy is predicted to be appreciable.The results of the calculations are analysed by comparison with experimental data on the benzene crystal at low temperature. A consistent interpretation of both magnetic resonance results and the triplet~ singlet absorption spectrum is obtained.

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“…The calculations reported by van der Waals et al [6] were aimed in particular at providing a quantitative interpretation of two observations made in recent low-temperature work on isotopically mixed benzene crystals: the non-hexagonality of the electron spin distribution in the phosphorescent triplet state [7,8] and the remarkable low-frequency doublet in the triplet+-singlet absorption spectrum [9]. With a model in which only the dominant e2g mode v s (mainly C-C stretching) was considered, these seemingly different phenomena could be explained from a single point of view.…”

Section: Introductionmentioning

confidence: 99%

Vibronic interaction in the lower electronic states of benzene

Egmond

Waals²

1974

Molecular Physics

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Results are given of some calculations on the (pseudo Jahn-Teller) vibronic interaction between the lower excited Blu and Elu triplet states of benzene in which two active vibrations in the pseudo-cylindrical approximation are considered. A satisfactory account is given of the relative intensities of the six characteristic bands in the phosphorescence spectrum which involve one or three quanta of the active modes, and also of the energy of the prominent doublet in the absorption spectrum first observed by Burland et al. In addition interaction with a crystal field is considered: a simple potential affords a quantitative explanation of the splitting of the doublet in the absorption spectrum and also of the crystal field induced intensities of the 0-0 bands in absorption and emission.

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Electron Nuclear Double Resonance in Photoexcited Triplet-State Benzene-h6 Molecules in Benzene-d6 Single Crystals

Cited by 60 publications

References 7 publications

EPR of photo-excited triplet states: A personal account

EPR of photo-excited triplet states: A personal account

Vibronic interaction in the lower electronic states of benzene

Vibronic interaction in the lower electronic states of benzene

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