Ionization signal

Fig. 3.21 Characteristic relation of the ionization signal and the primary air ratio. 

In fuel-lean premixed burners, the primary air ratio determines the quality of combustion changing the rotational speed of the flue gas fan has also some influence. An ionization probe is used to determine the quality of combustion. A dedicated system, developed at GWI, provides accurate detection and analysis of the ionization signal. This includes a metering device, which is provided with a rectangular supply voltage, thus warranting very accurate ionization signals. 

Figure 2.6 CHjNHj vibrational spectra (a) H action spectrum obtained via 243.135 nm dissociation of vibrationally excited molecules and (b) ionization-loss stimulated Raman spectroscopy exhibiting the depletion of parent molecule ionization signal due to vibrational preexcitation. Reproduced with permission from Ref. [86]. Copyright (2009) AlP Publishing LLC.

Fig. 2. Ionization signals S( T) as functions of the pump-probe delay T. CH3CN -Nal is shown on the left panel (a) and CH3CN---CsI on the right panel (b). The probe duration and wavelength are 50 fs (FWHM) and 315 nm for Nal and 378 nm for Csl.

When the pulsed-field ionization signal of a single excited Rydberg peak is measured as a function of the delay time between the extraction field pulse... 

Figure 10. The N ion time-of-flight profile following Rydbeig state excitation around n = 150 (N = 2) in the presence of a 0.3-V/cm retarding field. The dotted line shows the one-color direct ionization signal, which is subtracted from the total signal in the analysis of the results.

At larger radii, eight-photon, above-threshold ionization (ATI), and a small amount of nine-photon (two-photon ATI) are observed. These are labeled as 8hv and 9hv in Figure 8A. These signals are very weak and the intensity is distributed over many vibrational levels. Within the first abovethreshold ionization signal (corresponding to eight-photon ionization) one... 

Fig. 7.12 Ratio of the signal resulting from ionization of m = 2 states (upper curve), and ionization of m = 0 states (lower curve) to the total ionization signal as a function of the slew rate from low to intermediate fields following excitation of the 34dj/2 state via the 3pifl state with o polarization (from ref. 16).

Fig. 10.4 Field ionization signal ( ) and 15 GHz microwave ionization signal ( ) for the Na 20s state showing the ionization threshold as both the disappearance of the field ionization signal and the appearance of the microwave ionization signal with increasing microwave power (decreasing attenuation). For convenience the microwave-field amplitude is also...

The experiment is done using the apparatus shown in Fig. 10.2. Two tunable dye lasers are used to excite K atoms in a beam to the (n + 2)s state. A static field can be applied to vary the separation between the 18s and (16,k) states. The atoms are exposed to a microwave pulse, and subsequently to a field ionization pulse which ionizes atoms in the (n,k) Stark state, but not those in the (n + 2)s state. The (n,k) field ionization signal is then monitored as either the microwave field amplitude or the static field is swept over many shots of the laser. To the extent that both Stark shifts are linear, the static field alters the energy separation between the two states, but not their wavefunctions. 

Fig. 10.14 Ionization signal of He 28s 3S atoms as a function of the peak electric field inside the cavity. The size of the vertical scale corresponds to approximately 1/3 of the saturated signal. Inset the calculated transition probability from the 28s 3S to the 29s 3S state after...

Equally as interesting as the size of the total cross section is the distribution of the final states subsequent to mixing. Examining the adiabatic field ionization signals of Kachru et al., 30 it appears that only the lowest Stark states nearest to the... 

Fig. 11.14 Field ionization signal when the Xe 27f state is populated as a function of ionizing field strength (a) without NH3, (b) with 10 5 Torr NH3. The resonant rotational NH3 transitions are indicated beneath each field ionization feature (from ref. 63).

The most easily observed process with ionic, as with neutral, collisions partners is mixing. When the Na nd states are exposed to an ion beam, the field ionization signal changes from one which is predominantly adiabatic to one which is predominantly diabatic. By measuring the fraction R of signal transferred from the adiabatic to the diabatic peak of the field ionization signal MacAdam et al. measured the depopulation cross section of the Na nd states by He+ ions.1 In the limit of small values of R the depopulation cross section is given by1... 

T, the absolute value of the cross section for 450 eV He+ is determined to be 2.6 x 108 A2 for n = 28. The fact that the higher n cross sections at the ion energy of 450 eV fall below the n5 dependence was later found to be an artifact due to insufficient resolution of the diabatic and adiabatic field ionization signals.2 In later experiments with other ions the n5 dependence shown in Fig. 13.2 was also observed.2,3 The later measurements also verified that the cross section was independent of ion species as long as the ions had the same velocity. Using ions of... 

Fig. 13.4 Diabatic field ionization signals for i changing under increasing incident beam intensities. For clarity the successive curves are displaced upward by one scale unit. Data points are taken from the transient digitizer records, and a small sloping background has been subtracted. Full curves are fits to the model of MacAdam et al. (from ref. 8).

One of the most interesting aspects of the study of the Na ns and np states is the distribution of final states. In Fig. 13.5 we show the field ionization signals obtained when the 39p, 40s, 39d, and 40p states are exposed to 43 eV Na+ ions.10 There is an initial adiabatic peak and a later broader diabatic feature. The Na+ current is more than adequate to depopulate the 39d state, and the 39d signal presumably reflects substantial population of the higher , m states of n = 39, due to both non-dipole low velocity collisions and multiple collisions. As shown by... 

Using two pulsed tunable dye lasers, Na atoms in a beam are excited to an optically accessible ns or ml state as they pass between two parallel plates. Subsequent to laser excitation the atoms are exposed to millimeter wave radiation from a backward wave oscillator for 2-5 [is, after which a high voltage ramp is applied to the lower plate to ionize selectively the initial and final states of the microwave transition. For example, if state A is optically excited and the microwaves induce the transition to the higher lying state B, atoms in B will ionize earlier in the field ramp, as shown in Fig. 16.5. The A-B resonance is observed by monitoring the field ionization signal from state B at fB of Fig. 16.5 as the microwave frequency is swept. 

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