Deflection of Indole

4.4 Deflection of Indole

The following measurements describe the behavior of indole in a strong inhomoge-neous electric field. Spatial profiles of indole are taken at different deflector voltages.

Spatial profile means to scan the height of the molecular beam with respect to the laser focus. Two spatial profiles at different deflector voltages are shown in fig. [4.10].

The black curve shows the spatial profile of indole without deflector voltage, whereas the red curve shows the spatial profile at 24 kV deflector voltage. To determine the deflection, the profiles are fitted assuming a Gaussian shape and determining the maximum position for each profile. An example for the fit of a Gaussian shape to the spatial profile is shown in [A.4]. The deflection for the red curve in fig. [4.10] is 0.33 mm from the black curve.

For the deflection of indole no simulations have been done, but the deflection of 0.33 mm at a deflector voltage of 24 kV matches the magnitude from deflection profiles of indole presented in [19].

The negative deflection shown in figure [4.10] shows a deflection upwards, because the molecular beams with respect to the laser focus has to be moved downwards.

For further demonstration of the spatial deflection, the position of the maxima are taken to get the deflection dependence on the deflector voltage. The result is shown in fig. [4.11]

hi

Fig. 4.10: Spatial profiles of indole at two different deflector voltages. The black data show the spatial profile with zero deflector voltage. The red data show the spatial profile at 24 kV deflector voltage. The deflection is 0.33 mm.

Fig. 4.11: Deflection profile of indole. The deflection is shown dependent on the deflector voltage.

A deflection of up to 0.4 mm at 24 kV deflector voltage is measured.

Chapter 5 Conclusion

The aim of this thesis to generate UV pulses for R2PI measurements of indole is achieved.

With the nonlinear processes second harmonic generation and sum frequency gen-eration UV pulses are generated from a Ti:Sapphire laser by using BBO-crystals.

The central wavelength of the generated UV pulses is at 266.5 nm with a bandwidth of 2.94 nm. An energy conversion efficiency of 6 % of the fundamental energy is achieved. The maximum energy which can be used for producing UV pulses is 585 µJ and the resulting UV energy is 34 µJ.

The cross correlation which is used for measuring the pulse duration does not give a result due to the missing temporal overlap. Several techniques do not give a result, neither. The theoretical minimum pulse duration of 35 fs due to the spectrum gives positive evidence for a short pulse duration.

TOF REMPI measurements of indole are taken at 800 nm IR and 269 nm UV pulses. The mass spectra show differences in the fragmentation. When ionizing in-dole with UV pulses via R2PI nearly no fragmentation occurs. This gives evidence for an electronic intermediate state which is excited by these UV pulses.

Additionally, the spatial deflection of indole in electrostatic fields is measured. At an applied deflector voltage of 24 kV the spatial deflection of the molecular beam is 0.4 mm.

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