Ionization and dissociation dynamics of vinyl bromide probed by femtosecond extreme ultraviolet transient absorption spectroscopy.

Strong-field induced ionization and dissociation dynamics of vinyl bromide, CH₂=CHBr, are probed using femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy. Strong-field ionization is initiated with an intense femtosecond, near infrared (NIR, 775 nm) laser field. Femtosecond XUV pulses covering the photon energy range of 50-72 eV probe the subsequent dynamics by measuring the time-dependent spectroscopic features associated with transitions of the Br (3d) inner-shell electrons to vacancies in molecular and atomic valence orbitals. Spectral signatures are observed for the depletion of neutral C₂H₃Br, the formation of C₂H₃Br+ ions in their ground (X ) and first excited (à ) states, the production of C₂H₃Br⁺⁺ ions, and the appearance of neutral Br (²P_3/2) atoms by dissociative ionization. The formation of free Br (²P_3/2) atoms occurs on a timescale of 330 ±150 fs. The ionic à state exhibits a time-dependent XUV absorption energy shift of ∼0.4 eV within the time window of the atomic Br formation. The yield of Br atoms correlates with the yield of parent ions in the à state as a function of NIR peak intensity. The observations suggest that a fraction of vibrationally excited C₂H₃Br⁺ (à ) ions undergoes intramolecular vibrational energy redistribution followed by the C-Br bond dissociation. The C₂H₃Br⁺ (X) products and the majority of the C₂H₃Br⁺⁺ ions are relatively stable due to a deeper potential well and a high dissociation barrier, respectively. The results offer powerful new insights about orbital-specific electronic processes in high field ionization, coupled vibrational relaxation and dissociation dynamics, and the correlation of valence hole-state location and dissociation in polyatomic molecules, all probed simultaneously by ultrafast table-top XUV spectroscopy. [ABSTRACT FROM AUTHOR]