Photodissociation Dynamics of 1,2-Diiodotetrafluoroethane Captured with Femtosecond Gas Phase Electr
Graduate Student Seminar
12:30 pm
Jorgensen Hall Room: 145
***This event is for graduate students only***
Presenter: Kyle Wilkin
Abstract
We have used ultrafast electron diffraction (UED) to capture the structural dynamics during the UV photodissociation reaction of 1,2-Diiodotetrafluoroethane (C2F4I2). The experiment was performed at the SLAC UED facility with a 3.7 MeV electron beam where previous experiments have shown femtosecond resolution [1][2]. Previously, H. Ihee et al. used UED with 5 ps resolution to study the evolution of photo-dissociated C2F4I2 and found the structure of the transient state C2F4I to be the classical non-bridged structure [3]. No evidence of a bridged structure was found; however, a question remained on whether a bridged structure with a femtosecond lifetime also existed. The Ihee experiment also observed a fraction of the transient C2F4I further dissociating to form C2F4 with a time constant of 30 ps. We have observed that the non-bridged structure forms within 200 fs of the laser excitation, without the iodine atom ever moving into the bridged position. We have determined this by following the position of the dissociating iodine wavepacket as it moves away from the molecule. After the first iodine dissociates we observe no evidence that the transient further dissociates to C2F4, in contrast with the earlier experiment. After dissociation an oscillation with a 200 fs period is observed in the inter-atomic distances of the transient. This oscillation is likely a fundamental stretch of one of the bonds, a beating between multiple fundamentals, or a rotation of CF2 with respect to the remaining CF2I. These findings are in good agreement with numerical simulations of the dissociation trajectories and work is still being done to extract the underlying nature of the periodic motion observed in the C2F4I after dissociation.
References:
[1] J. Yang, M. Guehr, X. Shen, R. Li, T. Vecchione, R. Coffee, J. Corbett, A. Fry, N. Hartmann, and C. Hast et al., Phys. Rev. Lett. 117, 153002 (2016).
[2] J. Yang, M. Guehr, T. Vecchione, M. S. Robinson, Renkai Li, N. Hartmann, X. Shen, R. Coffee, J. Corbett, A. Fry, K. Gaffney, T. Gorkhover, C. Hast, K. Jobe, I. Makasyuk, A. Reid, J. Robinson, S. Vetter, F. Wang, S. Weathersby, C. Yoneda, M. Centurion & X. Wang, “Diffractive imaging of a rotational wavepacket in nitrogen molecules with femtosecond megaelectronvolt electron pulses,” Nature Communications 7 (2016).
[3] H. Ihee, B. M. Goodson, R. Srinivasan, V. A. Lobastov, and A. H. Zewail, J. Phys. Chem. A 106, 4087-4103 (2002).
Presenter: Kyle Wilkin
Abstract
We have used ultrafast electron diffraction (UED) to capture the structural dynamics during the UV photodissociation reaction of 1,2-Diiodotetrafluoroethane (C2F4I2). The experiment was performed at the SLAC UED facility with a 3.7 MeV electron beam where previous experiments have shown femtosecond resolution [1][2]. Previously, H. Ihee et al. used UED with 5 ps resolution to study the evolution of photo-dissociated C2F4I2 and found the structure of the transient state C2F4I to be the classical non-bridged structure [3]. No evidence of a bridged structure was found; however, a question remained on whether a bridged structure with a femtosecond lifetime also existed. The Ihee experiment also observed a fraction of the transient C2F4I further dissociating to form C2F4 with a time constant of 30 ps. We have observed that the non-bridged structure forms within 200 fs of the laser excitation, without the iodine atom ever moving into the bridged position. We have determined this by following the position of the dissociating iodine wavepacket as it moves away from the molecule. After the first iodine dissociates we observe no evidence that the transient further dissociates to C2F4, in contrast with the earlier experiment. After dissociation an oscillation with a 200 fs period is observed in the inter-atomic distances of the transient. This oscillation is likely a fundamental stretch of one of the bonds, a beating between multiple fundamentals, or a rotation of CF2 with respect to the remaining CF2I. These findings are in good agreement with numerical simulations of the dissociation trajectories and work is still being done to extract the underlying nature of the periodic motion observed in the C2F4I after dissociation.
References:
[1] J. Yang, M. Guehr, X. Shen, R. Li, T. Vecchione, R. Coffee, J. Corbett, A. Fry, N. Hartmann, and C. Hast et al., Phys. Rev. Lett. 117, 153002 (2016).
[2] J. Yang, M. Guehr, T. Vecchione, M. S. Robinson, Renkai Li, N. Hartmann, X. Shen, R. Coffee, J. Corbett, A. Fry, K. Gaffney, T. Gorkhover, C. Hast, K. Jobe, I. Makasyuk, A. Reid, J. Robinson, S. Vetter, F. Wang, S. Weathersby, C. Yoneda, M. Centurion & X. Wang, “Diffractive imaging of a rotational wavepacket in nitrogen molecules with femtosecond megaelectronvolt electron pulses,” Nature Communications 7 (2016).
[3] H. Ihee, B. M. Goodson, R. Srinivasan, V. A. Lobastov, and A. H. Zewail, J. Phys. Chem. A 106, 4087-4103 (2002).