Optical and Zeeman studies of the first excited singlet state of zinc porphin in a single crystal ofn-octane: Evidence for Jahn-Teller instability
- 1 December 1972
- journal article
- research article
- Published by Taylor & Francis in Molecular Physics
- Vol. 24 (6), 1203-1215
- https://doi.org/10.1080/00268977200102291
Abstract
The absorption and fluorescence spectra of Zn porphin in an n-octane single crystal at 4·2 K are reported in the region between 17 400 and 18 500 cm-1. A strong peak appears in both spectra at 17 961 cm-1 and is assigned to the origin of one component (|x, 0>) of the nearly degenerate Q-band. In absorption a second strong line occurs at a frequency δ = 109 cm-1 above the first; a corresponding line is almost totally absent in the emission spectrum at 4·2 K, but it appears as a hot band of appreciable intensity when the temperature is raised to 80 K. This feature is assigned to the origin of the other component (|y, 0>) of the Q-band. The lifting of the degeneracy of the Q-band is interpreted as a crystal field splitting of the Jahn-Teller unstable 1 Eu state. The Zeeman effect is investigated for the 0–0 transition of the phosphorescence spectrum and the |x, 0> and |y, 0> components of the Q-band absorption spectrum. From the phosphorescence experiment it is concluded that the great majority of the ZnP guests are oriented in the host with an angle of about 25° between the out-of-plane molecular axes and the crystal a-axis. The analysis of the Zeeman effect in absorption (H//crystal a-axis) is complicated by the Jahn-Teller instability which causes two additional unknowns to appear in the problem: the frequency ν and the nuclear displacement parameter α of the active mode. When not making an assumption about these parameters one can only derive a lower limit for the matrix element of the orbital angular momentum between the two electronic components: Λ > 4·6. If is identified with the low-frequency mode of 180 cm-1 appearing in the absorption spectrum, then it follows that Λ = 6·1 ± 0·6 with α = 1·4 ± 0·1.Keywords
This publication has 18 references indexed in Scilit:
- The zeeman effect in the benzene 3B1u state. Evidence for a dynamic pseudo-jahn—teller distortionChemical Physics Letters, 1971
- Zeeman Effect in Porphyrins: Zero-Field Splitting of the Excited Electronic StatesThe Journal of Chemical Physics, 1971
- The lowest triplet state of Zn porphinMolecular Physics, 1971
- Singlet–Triplet Absorption of Crystalline Naphthalene by High-Resolution Photoexcitation SpectroscopyThe Journal of Chemical Physics, 1969
- The Zeeman effect in porphyrinsJournal of Molecular Spectroscopy, 1968
- Spectra of porphyrinsJournal of Molecular Spectroscopy, 1965
- Indirect Observation of Singlet—Triplet Absorption in Anthracene CrystalsThe Journal of Chemical Physics, 1963
- Study of the Effects of Substitution on the Absorption Spectra of PorphinThe Journal of Chemical Physics, 1959
- Molecular Orbital Calculations on Porphine and TetrahydroporphineThe Journal of Chemical Physics, 1950
- On the Theory of the π-Electron System in PorphinesThe Journal of Chemical Physics, 1949