Coulomb-explosion imaging of concurrent CH2BrI photodissociation dynamics

Abstract

The dynamics following laser-induced molecular photodissociation of gas-phase CH 2 BrI at 271.6 nm were investigated by time-resolved Coulomb explosion imaging using intense near-IR femtosecond laser pulses. The observed delay-dependent photofragment momenta reveal that CH 2 BrI undergoes C-I cleavage, depositing 65.6% of the available energy into internal product states, and that absorption of a second UV photon breaks the C-Br bond of CH 2 Br. Simulations confirm that this mechanism is consistent with previous data recorded at 248 nm, demonstrating the sensitivity of Coulomb explosion imaging as a real-time probe of chemical dynamics.2

Imaging the Dynamics of CH2BrI Photodissociation in the Near Ultraviolet Region

“…concluded that 30% of the available energy is imparted to translation following 248 nm photolysis of CH 2 BrI by assuming the C-I bond dissociation enthalpy to be the same as CH 3 I calculated from heats of formation. Additionally, using femtosecond, near-infrared laser pulses with Coulomb explosion imaging, Burt and co-workers ascertained that 66% of the available energy is deposited into the CH 2 Br radical following CH 2 BrI ground-state dissociation, in accord with the current results 11.…”

“…Therefore, the near-UV region is dominated by two channels forming I atoms either in the ground state [I As a bichromophoric molecule, CH 2 BrI has been the subject of previous experimental studies focusing on the excited state, bond-selective fragmentation towards I/I* and Br/Br*. [7][8][9][10][11] Lee and Bersohn investigated the photodissociation of CH 2 BrI with a broadband light source extending from 240 to 340 nm using mass spectrometry, and reported rapid photodissociation with a measured anisotropy of β = 1.42 ± 0.14 from I atom products. 7 Butler and co-workers performed photofragment translational spectroscopy to measure the branching to I/I*, Br/Br*, and IBr following excitation at 193, 210 and 248 nm.…”

Time-resolved ion imaging at free-electron lasers using TimepixCam

“…TimepixCam timecodes are shown on the top horizontal axis, with the lower horizontal axis showing the time in nanoseconds. or I 2+ ions that are produced with a neutral co-fragment, for example if the molecule is first UV-dissociated and then post-ionized by the NIR pulse (Burt et al, 2017). This feature is also visible in the images from the UV-FEL pump-probe run (bottom row in Fig.…”

“…To demonstrate the capabilities and advantages of combining TimepixCam with a velocity-map imaging setup for pumpprobe experiments with free-electron lasers and optical lasers, we present data on the UV-induced dissociation of gas-phase CH 2 IBr probed by time-resolved Coulomb explosion imaging as an example. A more detailed discussion of the results and conclusions from the experiment is given by Burt et al (2017) and Kö ckert et al (2018).…”

Time-resolved photoelectron angular distributions from nonadiabatically aligned CO2 molecules with SX-FEL at SACLA

“…The first imaging of atomic motions during photochemical processes has been achieved by the ultrafast electron diffraction (UED) [10][11][12] and the ultrafast x-ray diffraction (UXD) [13][14][15][16]. Other imaging techniques such as the Coulomb explosion imaging (CEI) [17][18][19][20], the laser-induced electron diffraction (LIED) [21][22][23], and the ultrafast x-ray photoelectron diffraction (UXPD) [24][25][26][27][28][29][30][31][32][33][34][35][36] are also in progress. Among them, characteristic features of the XPD are element-specific and chemical-state-specific.…”