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Primary photochemical processes in hexafluorobiacetyl Reid, William John
Abstract
Absolute photochemical quantum yields of hexafluoro-biacetyl vapour have been obtained at various exciting wavelengths between 250 and 440 nm over the range 0.5 - 400 torr. The yields are strongly dependent on pressure demonstrating that vibrational relaxation is the dominant process competing with unimolecular dissociation. It is found that two different states contribute to dissociation. One is identified as the excited singlet level reached on excitation. The other is attributed to the vibronic level reached on intersystem crossing from that initially formed vibronic state. The intersystem crossing rate constant has been shown to be a strong function of excitation energy. It is postulated that the first excited singlet state of hexafluorobiacetyl is photochemically inert unless it has at least 70 kcal of vibronic energy. This accounts for no decomposition being observed at the higher wavelengths. Temperature and quenching studies have shown that the equilibrated triplet state is unreactive photochemically. Phosphorescence lifetime measurements at very low pressures have confirmed that wall-deactivation for the relatively long lived equilibrated triplet species is important when the average distance which the triplet molecule can diffuse is of the same magnitude as the cell radius. The data from the various investigations are combined to give a description of the primary photochemical and photo-physical events. From this information a mechanism for the primary process in hexafluorobiacetyl is proposed and critically evaluated. Estimates of the specific rate constants for the photochemical processes are given and discussed.
Item Metadata
Title |
Primary photochemical processes in hexafluorobiacetyl
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1972
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Description |
Absolute photochemical quantum yields of hexafluoro-biacetyl vapour have been obtained at various exciting wavelengths
between 250 and 440 nm over the range 0.5 - 400 torr. The yields are strongly dependent on pressure demonstrating that vibrational relaxation is the dominant process competing with unimolecular dissociation.
It is found that two different states contribute to dissociation. One is identified as the excited singlet level reached on excitation. The other is attributed to the vibronic level reached on intersystem crossing from that initially formed vibronic state. The intersystem crossing rate constant has been shown to be a strong function of excitation energy. It is postulated that the first excited singlet state of hexafluorobiacetyl is photochemically inert unless it has at least 70 kcal of vibronic energy. This accounts for no decomposition
being observed at the higher wavelengths. Temperature
and quenching studies have shown that the equilibrated triplet state is unreactive photochemically. Phosphorescence lifetime measurements at very low pressures have confirmed that wall-deactivation for the relatively long lived equilibrated
triplet species is important when the average distance which the triplet molecule can diffuse is of the same magnitude
as the cell radius.
The data from the various investigations are combined to give a description of the primary photochemical and photo-physical events. From this information a mechanism for the primary process in hexafluorobiacetyl is proposed and critically
evaluated. Estimates of the specific rate constants for the photochemical processes are given and discussed.
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Genre | |
Type | |
Language |
eng
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Date Available |
2011-03-24
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0060047
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.