I  U  P  A  C






News & Notices

Organizations & People

Standing Committees

Divisions

Projects

Reports
..By Year
..By Division
..Other Committees
..Provisionals

Publications

Symposia

AMP

Links of Interest

Search the Site

Home Page

Pure Appl. Chem., Vol. 68, No.12, pp. 2223-2286, 1996

Glossary of Terms Used in Photochemistry


[A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M]
[N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] [X] [Y] [Z]


Q- SWITCHED LASER
A laser in which the state of the device introducing important losses in the resonant cavity and preventing lasing operation is suddenly switched to a state where the device introduces very low losses. This increases rapidly the Quality factor of cavity, allowing the build-up of a short and very intense laser pulse. Typical pulse durations are in the ns range. The Q-switching may be active (a rotating mirror or electro-optic device) or passive (a saturable absorber).

See also free-running laser.

QUANTUM (of radiation)
An elementary particle of electromagnetic energy in the sense of wave-particle duality.

See photon.

QUANTUM COUNTER
A medium emitting with a quantum yield independent of the excitation energy over a defined spectral range (e.g., concentrated rhodamine 6G solutions between 300 and 600 nm). Also used for devices producing an electrical signal proportional to the photon flux absorbed in a medium.

QUANTUM EFFICIENCY

See efficiency.
For a primary photochemical process, quantum efficiency is identical to quantum yield.

QUANTUM YIELD (phi)

The number of defined events which occur per photon absorbed by the system. The integral quantum yield is

For a photochemical reaction,

The differential quantum yield is

where d[x]/dt is the rate of change of a measurable quantity, and n the amount of photons (mol or its equivalent einstein) absorbed per unit time. phi can be used for photophysical processes or photochemical reactions.

See also efficiency.

QUARTET STATE
A state having a total spin quantum number equal to 3/2.

See multiplicity.

QUARTZ-IODINE LAMP
A tungsten filament high-intensity incandescent lamp which contains iodine a quartz envelope. Used primarily as a source of visible light.

QUENCHER
A molecular entity that deactivates (quenches) an excited state of another molecular entity. either by energy transfer, electron transfer, or by a chemical mechanism.

See quenching, Stern-Volmer kinetic relationships.

QUENCHING
The deactivation of an excited molecular entity intermolecularly by an external environmental influence (such as a quencher) or intramolecularly by a substituent through a nonradiative process. When the external environmental influence (quencher) interferes with the behavior of the excited state after its formation, the process is referred to as dynamic quenching. Common mechanisms include energy transfer, charge transfer, etc. When the environmental influence inhibits the excited state formation the process is referred to as static quenching.

See Stern-Volmer kinetic relationships.

QUENCHING CONSTANT

See quencher, quenching, Stern-Volmer kinetic relationships.





[A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M]
[N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] [X] [Y] [Z]

> Return to Index Page

Online version compiled by European Photochemistry Association (EPA)


Page last modified 31 August 2000.
Copyright ©1999 International Union of Pure and Applied Chemistry.
Questions or comments about IUPAC, please contact, the Secretariat.
Questions regarding the website, please contact Web Help.