Observation of Hydrogen Migration in Cyclohexane under an Intense Femtosecond Laser Field

We experimentally demonstrate hydrogen migration in photoionization and photofragmentation processes of cyclohexane (C₆H₁₂) under a near-infrared (800 nm) intense femtosecond laser field by the dc-slice imaging technique, and the observation of fragment ions CH₃⁺, C₂H₅⁺, and C₃H₇⁺ can be regarded as direct evidence that chemical bond rearrangement processes associated with hydrogen migration occur in the dissociative ionization process of cyclohexane. We measure the sliced images of fragment ions CH₃⁺, C₂H₅⁺, and C₃H₇⁺ and calculate their corresponding kinetic energy release (KER) and angular distributions, and it is confirmed that high-KER components of these fragment ions result from two-body Coulomb explosion of the doubly charged parent ion C₆H₁₂²⁺ whereas low-KER components result from dissociative ionization of the singly charged parent ion C₆H₁₂⁺. Moreover, we measure the maximally attainable relative yields of fragment ions CH₃⁺, C₂H₅⁺, and C₃H₇⁺, which approach 4.5%, 4.0%, and 3.0%, respectively.