Conventional Microsecond Flash Photolysis

1000 nm. This technique is still important for the measurement of high-resolution absorption spectra of free radicals and excited molecules in the gas phase. In the conventional technique which is limited to the, s time-scale, the delay between the photolytic flash and the monitoring flash is set by an electronic device (called the delay unit). 

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This follows the ionisation potential of the amino groups. Both conventional and microsecond flash photolysis confirmed the involvement of intramolecular hydrogen atom abstraction and this is illustrated by the mechanistic processes in scheme 3 for an N-methyl derivative and scheme 4 for a diethylamino derivative. Here it is seen that the N-methylpiperazine derivative, does not undergo intermolecular hydrogen atom abstraction. Intramolecular hydrogen... 

An intense short pulse of UV or visible radiation is used to electronically excite the sample, and the subsequent absorption changes are probed spectrophotomet-rically. The technique was first introduced by Norrish and Porter in 1949 [18] and at this time gas-filled discharge lamps were used, limiting the time resolution, which is principally governed by the duration of the excitation pulse, to microseconds. This is now usually termed conventional flash photolysis. However, with the development of laser pulsed techniques in place of flash excitation, the time resolution has been progressively reduced to subpicosecond, particularly with the use of mode-locked solid state lasers. Much current work utilises nanosecond time resolution with pulsed lasers such as ruby, neodymium and excimer lasers. 

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