Dissociative ionization of benzene in intense ultra-fast laser pulses

Abstract

Based on the possibility of multiphoton ionization of the inner valence electrons in polyatomic molecules, a model was proposed to predict the abundance of different fragments resulting from dissociative ionization of the polyatomic molecules interacting with short laser pulses. According to this model the fragmentation of these molecules occurs through multiphoton ionization of the inner valence electrons, which results in a molecular ion in an excited state. Through radiationless transition the population is transferred to the highly excited levels of the ground electronic state. The molecular ion created in this manner is not stable and dissociates rapidly. To test the applicability of the model, the fragmentation of a benzene molecule interacting with linearly and circularly polarized Ti:sapphire laser pulses was studied. The model was tested by comparing the measured laser-intensity-dependent abundance of C 4 H + 4 fragment ions with the calculated ones and excellent agreement was obtained with the experimental results.

Ultrafast REMPI in benzene and the monohalobenzenes without the focal volume effect

“…The six-photon result matches previous results carried out at 800 nm. 25 In fluorobenzene and chlorobenzene we observe a sevenphoton to four-photon absorption, indicative of (3+4) REMPI. This seems counterintuitive, as the ionization potential of both molecules (9.20 eV and 9.07 eV for fluorobenzene and chlorobenzene, respectively) are within the energy of six photons.…”

“…The structures in our measured ion yields at B2 Â 10 13 W/cm 2 are washed out in ref. 25 due to integration over the focal volume. Additionally, for intensities beyond B10 14 W/cm 2 our ion yield decreases due to competing processes, such as multiple ionization and fragmentation.…”

Analytical model for calibrating laser intensity in strong-field-ionization experiments

“…Ionization of benzene without dissociation (by selecting C 6 H + 6 ions) has been reported earlier by Talebpour et al [64] using 200-fs, 800-nm laser pulses. Figure 7 shows their reported ionization yields, normalized to the ion yields calculated from the present molecular PPT theory at an intensity of 2 × 10 14 W/cm 2 .…”

“…The laser is a Gaussian pulse with wavelength of 800 nm and FWHM of 200 fs. The experimental data is from [64], and the two other model calculations are from Refs. [34] and [65].…”

Chirp and polarization control of femtosecond molecular fragmentation

“…Similarly, a vast amount of reported study on the effect of polarization on fragmentation shows a substantial suppression of fragmentation channel when polarization is altered from linear to circular for non-resonant dissociation [15][16][17][18][19][20][21][22]. Such suppression with circular polarization has been associated with electron re-scattering or re-collision (ERC) [23] though the molecular fragmentation pattern has been unaffected by laser polarization [24,25].…”