Lifetimes longer than microseconds

Ion lifetimes as long as milliseconds have been measured in a number of different ways. One of the earliest methods involved flight tubes some metres long along which the ions were passed at relatively low velocities and within which the decompositions studied occurred [817, 818, 878]. The trajectories were stabilized by electric radio frequency quadrupole fields. Ionization was by electron impact and decompositions of carbonium ions derived from alkanes were observed over the time range 1/is to 1 ms. 

The lifetimes of ions studied by ion cyclotron resonance (ICR) are commonly of the order of milliseconds [254], In terms of eqn. (9), the limits tx and t2 of the observation window are zero and of the order of milliseconds, respectively. Reactive ions of longer lifetimes are not distinguished from those with the more usually encountered lifetimes ( /is). Using ICR, it has been found that decomposition of the molecular ion of 1, 5-hexadiyne (c.f. Sect. 5.7) to lose H occurs predominantly at times greater than microseconds [344], An ICR mass spectrometer constituting the second half of a tandem mass spectrometer has been used to study decomposition of propane ions up to times of milliseconds [775], The observation window in this case extended from tx — /is to 

Ions can be trapped for times of the order of milliseconds in the space charge of electron beams within ion sources [96] and time-of-flight mass spectrometry permits not only the study of reactions at long times ( ps), but also at short times ( ps) [439, 728, 882]. 

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Cline-Love and Upton found microsecond natural lifetimes for 5,5-disubstituted barbiturates.69 This suggests that the fluorescence transition is of the n - n type, although the absorption should be of the n - n type. Moreover, natural lifetimes of the excited states for barbiturates with unsaturated substituents are longer than those for barbiturates with alkyl groups. A small mixing of electronic levels of the fluorophore with the levels of the electronic environment provided by the unsaturated substituents have been proposed to explain this phenomenon.69... 

Since the lifetimes of the Ge isomers are much longer than the microsecond anticoincidence times of standard instruments, the emitted lines are not vetoed by the shield. Thus the lines produced by the activation of Ge nuclei are the strongest in the... 

Phosphorescence is a longer-lived emission than fluorescence, with the former having lifetimes varying from microseconds (p,s = lO" s) to seconds, as compared with picoseconds (ps = 10" s) to nanoseconds (ns = 10 s) for the latter. Even though phosphorescence emission is a two-step process (inter-... 

For solvents in which the lifetime of the solvated electron is short, it cannot be observed in this way. For instance in water, the hydrated electron may be formed by dissolving alkali metals. But the metal dissolution timescale is much longer (a hundred of milliseconds) than the lifetime of the electron (a few microseconds) and, as soon as solvated electrons are produced, a very fast reaction occurs between two solvated electrons producing molecular hydrogen, leading to the explosive combustion in air that accounts for the hazardous contact of alkali metal and water. 

As before, let us first look at pulsed Ti sapphire lasers pumped by g-switched Nd YAG lasers. The overall resonator components are very much the same as for the tuneable dye laser. However, because of the much longer lifetime of the upper laser level (a few microseconds opposed to a few nanoseconds for laser dyes), the pumping geometry is now longitudinal rather than transverse. The pumping geometry is... 

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