Formation of fragment ions (H+, H3+, CH3+) from ethane in intense femtosecond laser fields – from understanding to control

Abstract

The dissociative ionization of ethane in intense femtosecond laser fields has been investigated as a function of the laser pulse shape by systematically varying the quadratic spectral phase, i.e. the linear chirp. A very pronounced effect of the sign of the chirp is observed for the parent ion and all fragment ion yields, all ion yields being strongly favored by negative chirp of the laser field. The ratio of the H₃⁺ ion yield to H⁺ ion yield can also be manipulated by changing the linear chirp, the maximum being observed for a significantly smaller chirp value than that for the individual ion yields. Since the H⁺ ions and the H₃⁺ ions predominantly originate from the dication of ethane, this indicates control of fragmentation within one charge state of the ethane. Additional experiments performed with d₃-ethane demonstrate that the control is operative prior to the statistical scrambling of hydrogen atoms, further supporting the concept of intra-charge-state control. In the case of formation of CH₃⁺ ions two different ensembles occur, one from the monocation, another from the dication. The ratio of these ensembles can again be controlled by means of the linear chirp parameter implying control between the two different charge states (inter-charge-state control).