The photodissociation dynamics of CH2I2 at 200 nm occurs through the sequential cleavage of both carbon-iodine bonds. These reactions were probed at the iodine 4d edge using the FLASH free electron laser. The large absorption cross section of iodine leads to site-selective ionisation by XUV pulses of one or both iodine substituents. These UV and XUV interactions can cause two- and three-body Coulomb explosions of the parent molecule and of the dissociating photofragments. The time-dependent and time-independent fragmentation pathways were characterised using covariance analysis. Parent ion explosions resulting in Coulombic repulsion between two multiply charged iodine cations and a neutral or charged methyl fragment were differentiated using recoilframe covariance, where the time-independent recoil between iodine ions is 180o in the former case, and 155o in the latter. The time dependence of the two-body explosion features were also used to investigate one- or two-bond dissociation pathways. The relative intensities of these two features reveal that the likelihood of charge transfer between the dissociating fragments and consequential three-body explosions, occurring on timescales competitive with Coulomb explosions, are dependent on the magnitude of the charges on the halogens.

Probing the photodissociation dynamics of CH2I2 at 200 nm using site-selective XUV ionisation

ACS Spring 2022

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