Wavelength dependence of the angular distribution of the Coulomb explosion in the femtosecond ionisation of methyl iodide

Abstract

The angular distribution of the ions coming from Coulomb explosion following femtosecond ionisation of methyl iodide is studied in the spectral range of 600 to 1450 nm. Under these conditions, iodine and methyl fragment ions are generated, both via dissociative ionisation and via Coulomb explosion following the double ionisation of the parent ion. However, the dependence of the angular distribution of the fragment ions on the ionisation wavelength is completely different for those two mechanisms: dissociative ionisation fragments are being ejected with high anisotropy, irrespectively of the wavelength, while the angular distribution of the Coulomb explosion fragments changes from anisotropic, for an excitation wavelength close to 600 nm, to isotropic close to 950 nm, and remain isotropic up to 1450 nm.

GRAPHICAL ABSTRACT

Keywords:

• Coulomb explosion
• alignment
• femtosecond laser
• VMI

Acknowledgments

D. S. wants to thank M. Kechaoglou for his valuable aid concerning the use of the OPA, P. Kalaitzis and E. Sakkoula for advise concerning the use of the finite analysis software, Dr. S. Danakas for giving access to the Abel transformation code used in this work and L. Rubio-Lago and C. Kosmidis for reading the manuscript and providing useful discussion. The experimental work was performed in the Central Laser Facility of University of Ioannina.

Disclosure statement

No potential conflict of interest was reported by the author(s).