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This study explores intramolecular hydrogen migration in acetonitrile dication under phase-controlled intense laser fields using three-dimensional coincidence ion momentum imaging. The findings reveal a phase-dependent fragment asymmetry in the two-body Coulomb explosion pathway, indicating that tunnel ionization preferentially aligns the methyl group with the weaker side of the laser field. Additionally, the observed deuteration effect highlights the significant influence of the two-color asymmetric laser field on the directionality of hydrogen migration, providing insights into molecular dynamics in intense laser environments.
Phase-controlled laser fields can dramatically alter the directionality of hydrogen migration in acetonitrile dication, revealing unexpected asymmetries in molecular fragmentation.
We investigate intramolecular hydrogen migration in acetonitrile dication in phase-controlled $\omega$-$2\omega$ intense laser fields (800 and 400 nm, 3.3$\times$10$^{14}$ W/cm$^2$) using three-dimensional coincidence ion momentum imaging. The two-body Coulomb explosion pathway, CH$_3$CN$^{2+}$ $\rightarrow$ CH$_3^+$ + CN$^+$, exhibits a clear phase-dependent fragment asymmetry along the laser polarization direction, showing that the tunnel ionization preferentially prepares the acetonitrile dication with the methyl group pointing toward the smaller amplitude side of the laser electric fields. The Coulomb explosion pathway occurring after the migration of a single hydrogen atom, CH$_3$CN$^{2+}$ $\rightarrow$ CH$_2^+$ + HCN$^+$, shows a pronounced reduction in the fragment asymmetry. A clear deuteration effect observed for the asymmetry of the hydrogen-migration pathway suggests that the two-color asymmetric laser field has a significant impact on directionality of intramolecular hydrogen migration in acetonitrile dication.
