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Inverse electronic relaxation and chromyl chrolide: the final conflict
99
Solid state hole-burning spectroscopy GERALD
J. SMALL,
Ames Laboratory
ROLAND
I’. STOUT
and JOHN M. HAYES
and Deparbnenr of Chemistry, Iowa State University, Ames IA 50011 (U.S.A.)
Apart from transient hole burning it is now well documented that persistent hole burning of the electronic absorption spectra of impurity molecules imbedded in organic solids occurs in a variety of systems. Both types of process owe their existence to the fact that the impurity vibronic absorption bands are site inhomogeneously broadened. Two mechanisms for persistent hole burning are discussed: photochemical and non-photochemical (photophysical). The photochemical mechanism is associated with impurity molecules which are intrinsically photoreactive so that a narrow-line laser can be utilized for persistent site-selective photobleaching. In this case both crystalline and amorphous host media can be employed. Non-photochemical hole burning occurs with photostable molecules but only when they are imbedded in amorphous media such as glasses and polymers. The hole-burning mechanism hinges on the disorder in the glass and involves phonon-assisted tunneling processes of impurity-glass disorder states. These processes can be viewed as impurity-glass quantum photoisomerization reactions. The Ames Laboratory is a U.S. Department of Energy facility.
Inverse electronic relaxation and chromyl chloride: the final conflict
J. NIEMAN*
Departmenl (U.S.A.)
and A.M.
of Chemistry,
RONN*
City University of New York at Brooklyn
College, Brooklyn,
NY 11210
Inverse electronic relaxation (IER) studies of chromyl chloride (CrO2C12) were extended to the collision-free regime (1 P - 1W5 Torr). The visible emission, which had been shown earlier to originate from the three distinct species Cr02C12, Cr02Cl - and CrOZ, was remeasured both spectrally and temporally. Laser excitation wavelength variations as well as the dependences on fluence and pulse duration were determined under collision-free conditions. These studies unequivocally establish the validity of parent fluorescence in Cr02Cl and just as clearly designate the conditions for IER in general. Of particular importance to
* Present address: LIC Industries Inc., P-0. Box 200, Suffern, NY 10901, U.S.A.
100 the continuing interest in this system are the collision-free lifetimes measured at 1O-5 Torr: t(CrOzClz) (6300 A) S 85,~s r(Crc&) (5300 A) z 130/N The lifetime of the radical was remeasured at the slightly higher pressure of 3 x lo4 Torr as r(Cr02C1*) S 52,~s.
Sdveut effects on the photochemistry of iodine in solution
THOMAS Universitit
DORFMULLER Bielefeid,
and
Fakultit
fir
MANFRED
Chemie,
Postfach
GEILHAUPT 8640,
48 Bielefeld
1 (F. R. G.)
The intermolecular potential of iodine mofecules in solution is strongly affected by the nature of the interaction with solvent molecules. As a consequence the energy disposal on absorption of light by the iodine molecules is markedly dependent on their environment, The radiationless deactivation, fluorescent light emission and photochemical dissociation pathways were studied by analysing absorption and resonance Raman spectra on the basis of the Franck-Condon overlap integrals for the excited states of the free iodine molecules. Thus the quantum yields of photochemicaI dissociation and of the resonance Raman process were used as indicators of the intermolecular perturbation in the liquid phase. As a result of this study we obtained information concerning the changes in the intramolecuiar potentiaI in the ground state and in the excited states resulting from intermolecular interactions with different partners.
Photochemical reactions in the solid phase observed by a holographic technique
CH. BRAUCHLE Institute D.M.
of Physical BURLAND
IBM Research
Chemirwy,
University
and
BJORKLUND
Laboratory,
G.C.
San Jo&,
of Munich,
Sophienswusse
II,
O-8000
Mfinchen
2 (F.R.G.)
CA (U.S.A.)
The technique of holographic photochemistry provides a convenient means of following the temporal course of a photochemical reaction in the solid phase. In this technique the course of the reaction is followed by monitoring the growth in intensity of a hologram produced by two interfering laser beams. The rate of
Solid state hole-burning spectroscopy GERALD
J. SMALL,
Ames Laboratory
ROLAND
I’. STOUT
and JOHN M. HAYES
and Deparbnenr of Chemistry, Iowa State University, Ames IA 50011 (U.S.A.)
Apart from transient hole burning it is now well documented that persistent hole burning of the electronic absorption spectra of impurity molecules imbedded in organic solids occurs in a variety of systems. Both types of process owe their existence to the fact that the impurity vibronic absorption bands are site inhomogeneously broadened. Two mechanisms for persistent hole burning are discussed: photochemical and non-photochemical (photophysical). The photochemical mechanism is associated with impurity molecules which are intrinsically photoreactive so that a narrow-line laser can be utilized for persistent site-selective photobleaching. In this case both crystalline and amorphous host media can be employed. Non-photochemical hole burning occurs with photostable molecules but only when they are imbedded in amorphous media such as glasses and polymers. The hole-burning mechanism hinges on the disorder in the glass and involves phonon-assisted tunneling processes of impurity-glass disorder states. These processes can be viewed as impurity-glass quantum photoisomerization reactions. The Ames Laboratory is a U.S. Department of Energy facility.
Inverse electronic relaxation and chromyl chloride: the final conflict
J. NIEMAN*
Departmenl (U.S.A.)
and A.M.
of Chemistry,
RONN*
City University of New York at Brooklyn
College, Brooklyn,
NY 11210
Inverse electronic relaxation (IER) studies of chromyl chloride (CrO2C12) were extended to the collision-free regime (1 P - 1W5 Torr). The visible emission, which had been shown earlier to originate from the three distinct species Cr02C12, Cr02Cl - and CrOZ, was remeasured both spectrally and temporally. Laser excitation wavelength variations as well as the dependences on fluence and pulse duration were determined under collision-free conditions. These studies unequivocally establish the validity of parent fluorescence in Cr02Cl and just as clearly designate the conditions for IER in general. Of particular importance to
* Present address: LIC Industries Inc., P-0. Box 200, Suffern, NY 10901, U.S.A.
100 the continuing interest in this system are the collision-free lifetimes measured at 1O-5 Torr: t(CrOzClz) (6300 A) S 85,~s r(Crc&) (5300 A) z 130/N The lifetime of the radical was remeasured at the slightly higher pressure of 3 x lo4 Torr as r(Cr02C1*) S 52,~s.
Sdveut effects on the photochemistry of iodine in solution
THOMAS Universitit
DORFMULLER Bielefeid,
and
Fakultit
fir
MANFRED
Chemie,
Postfach
GEILHAUPT 8640,
48 Bielefeld
1 (F. R. G.)
The intermolecular potential of iodine mofecules in solution is strongly affected by the nature of the interaction with solvent molecules. As a consequence the energy disposal on absorption of light by the iodine molecules is markedly dependent on their environment, The radiationless deactivation, fluorescent light emission and photochemical dissociation pathways were studied by analysing absorption and resonance Raman spectra on the basis of the Franck-Condon overlap integrals for the excited states of the free iodine molecules. Thus the quantum yields of photochemicaI dissociation and of the resonance Raman process were used as indicators of the intermolecular perturbation in the liquid phase. As a result of this study we obtained information concerning the changes in the intramolecuiar potentiaI in the ground state and in the excited states resulting from intermolecular interactions with different partners.
Photochemical reactions in the solid phase observed by a holographic technique
CH. BRAUCHLE Institute D.M.
of Physical BURLAND
IBM Research
Chemirwy,
University
and
BJORKLUND
Laboratory,
G.C.
San Jo&,
of Munich,
Sophienswusse
II,
O-8000
Mfinchen
2 (F.R.G.)
CA (U.S.A.)
The technique of holographic photochemistry provides a convenient means of following the temporal course of a photochemical reaction in the solid phase. In this technique the course of the reaction is followed by monitoring the growth in intensity of a hologram produced by two interfering laser beams. The rate of