Publications

1997
Guy Ashkenazi, Uri Banin, Allon Bartana, Ronnie Kosloff, and Sanford Ruhman. 1997. “Quantum Description of the Impulsive Photodissociation Dynamics of I^-~ 3 in Solution.” Advances in Chemical Physics, 100, Pp. 229-316. Publisher's Version
1994
Uri Banin, Allon Bartana, Sanford Ruhman, and Ronnie Kosloff. 1994. “Impulsive excitation of coherent vibrational motion ground surface dynamics induced by intense short pulses.” The Journal of chemical physics, 101, 10, Pp. 8461-8481. Publisher's Version Abstract

A framework for understanding impulsively photoinduced vibrational coherent motion on the ground electronic surface is presented. In particular strong resonant excitation to a directly dissociative electronic surface is considered. Three distinct approaches are employed. A two surface Fourier wavepacket method explicitly including the field explores this process in isolated molecules. A coordinate dependent two‐level system is employed to develop a novel analytical approximation to the photoinduced quantum dynamics. The negligible computational requirements make it a powerful interactive tool for reconstructing the impulsive photoexcitation stage. Its analytical nature provides closed form expressions for the photoinduced changes in the material. Finally the full simulation of the process including the solvent effects is carried out by a numerical propagation of the density operator. In all three techniques the excitation field is treated to all orders, allowing an analysis of current experiments using strong fields, resulting in substantial photoconversion. The emerging picture is that the impulsive excitation carves a coherent dynamical ‘‘hole’’ out of the ground surface density. A rigorous definition of the dynamical ‘‘hole’’ is constructed and used to define a measure of its coherence. In particular all photoinduced time dependence in the system can be directly related to the dynamical ‘‘hole.’’ All three techniques are used to simulate the pump probe experiment on the symmetric stretch mode of I3, including electronic and vibrational dephasing.

Uri Banin, Allon Bartana, Sanford Ruhman, and Ronnie Kosloff. 1994. “Impulsive excitation of coherent vibrational motion ground surface dynamics induced by intense short pulses.” The Journal of chemical physics, 101, 10, Pp. 8461-8481. Publisher's Version Abstract

A framework for understanding impulsively photoinduced vibrational coherent motion on the ground electronic surface is presented. In particular strong resonant excitation to a directly dissociative electronic surface is considered. Three distinct approaches are employed. A two surface Fourier wavepacket method explicitly including the field explores this process in isolated molecules. A coordinate dependent two‐level system is employed to develop a novel analytical approximation to the photoinduced quantum dynamics. The negligible computational requirements make it a powerful interactive tool for reconstructing the impulsive photoexcitation stage. Its analytical nature provides closed form expressions for the photoinduced changes in the material. Finally the full simulation of the process including the solvent effects is carried out by a numerical propagation of the density operator. In all three techniques the excitation field is treated to all orders, allowing an analysis of current experiments using strong fields, resulting in substantial photoconversion. The emerging picture is that the impulsive excitation carves a coherent dynamical ‘‘hole’’ out of the ground surface density. A rigorous definition of the dynamical ‘‘hole’’ is constructed and used to define a measure of its coherence. In particular all photoinduced time dependence in the system can be directly related to the dynamical ‘‘hole.’’ All three techniques are used to simulate the pump probe experiment on the symmetric stretch mode of I3, including electronic and vibrational dephasing.

Allon Bartana, Uri Banin, Sanford Ruhman, and Ronnie Kosloff. 1994. “Intensity effects on impulsive excitation of ground surface coherent vibrational motion: A ‘V’jump simulation.” Chemical physics letters, 229, 3, Pp. 211-217. Publisher's Version Abstract

Control of coherent ground surface dynamics is achieved by varying the intensity of a resonant ultrafast pump pulse. This pulse cycles amplitude between the ground and excited electronic surfaces resulting in a momentum kick and a coordinate dependent loss of amplitude, creating a nonstationary vibrational distribution: the ‘V’ jump. A qualitative change in composition occurs for intensities above π pulse conditions. The induced dynamics is observed by a delayed pulse which is dispersed and analyzed against time or as a two-dimensional frequency plot. Such an analysis makes it possible to distinguish the contributions of high vibrational harmonics to the dynamics.

1993
Uri Banin, Ronnie Kosloff, and Sanford Ruhman. 1993. “Femtosecond Chemical Dynamics in Solution: Photodissociation of I3‐.” Israel journal of chemistry, 33, 2, Pp. 141-156. Publisher's Version Abstract

We report a study of the UV photolysis of I3 in alcohol solutions, using femtosecond time‐resolved transient transmission experiments. We interpret our results to indicate that photoexcitation leads to direct formation, within 300 fs, of diiodide ions which are vibrating coherently. The time scales for vibrational dephasing, vibrational relaxation, and reorientation of the fragment ions are 400 fs, 4 ps, and 5 ps, respectively. UV transient transmission experiments were conducted in order to characterize the time scales for recombination. Recombination takes place on several time scales. A fast component is assigned to primary recombination, followed by vibrational relaxation on the ground state of I3. The prominence of this recombination route is found to be strongly dependent on the solvent. Finally, time domain quantum simulation techniques are employed in order to gain insight into the nature of the nascent diiodide vibrational distribution, and to introduce a semiquantitative model for the stage of bond fission for isolated ions.

Uri Banin and Sanford Ruhman. 1993. “Ultrafast photodissociation of I3. Coherent photochemistry in solution.” The Journal of chemical physics, 98, 6, Pp. 4391-4403. Publisher's Version Abstract

We report a comprehensive study of the UV photolysis of I3 in ethanol solution, using femtosecond time resolved transient transmission experiments. We interpret our results to indicate that with high probability, photoexcitation leads to direct formation of di‐iodide ions within 300 fs, which are vibrating coherently. Through our experiments we have been able to determine that the time scales for vibrational dephasing, vibrational relaxation, and reorientation of the fragment ions are 400 fs, 4 ps, and 5 ps, respectively. Transmission signals at 620 nm and at 880 nm, which are above and below the λmax of the known absorption of I2, oscillate at a precisely opposite phase. This and other results presented indicate that through the oscillations we are observing coherent vibration of the I2 photofragment. UV transient transmission experiments have been conducted in order to characterize the time scales for recombination. Preliminary results show that recombination takes place on several time scales. A fast component is assigned to primary recombination, followed by vibrational relaxation on the ground state of I3. The impulsive nature of the I3 photoexcitation induces coherent symmetric stretching vibration in the ground state tri‐iodide population. Finally, the large number of dynamical variables probed directly allows us to record the chronology of this reaction with unprecedented detail. We directly observe a new and potentially informative dynamical variable for this reaction—the absolute phase of fragment vibrations following the photodissociation.

Uri Banin and Sanford Ruhman. 1993. “Ultrafast photodissociation of I3. Coherent photochemistry in solution.” The Journal of chemical physics, 98, 6, Pp. 4391-4403. Publisher's Version Abstract

We report a comprehensive study of the UV photolysis of I3 in ethanol solution, using femtosecond time resolved transient transmission experiments. We interpret our results to indicate that with high probability, photoexcitation leads to direct formation of di‐iodide ions within 300 fs, which are vibrating coherently. Through our experiments we have been able to determine that the time scales for vibrational dephasing, vibrational relaxation, and reorientation of the fragment ions are 400 fs, 4 ps, and 5 ps, respectively. Transmission signals at 620 nm and at 880 nm, which are above and below the λmax of the known absorption of I2, oscillate at a precisely opposite phase. This and other results presented indicate that through the oscillations we are observing coherent vibration of the I2 photofragment. UV transient transmission experiments have been conducted in order to characterize the time scales for recombination. Preliminary results show that recombination takes place on several time scales. A fast component is assigned to primary recombination, followed by vibrational relaxation on the ground state of I3. The impulsive nature of the I3 photoexcitation induces coherent symmetric stretching vibration in the ground state tri‐iodide population. Finally, the large number of dynamical variables probed directly allows us to record the chronology of this reaction with unprecedented detail. We directly observe a new and potentially informative dynamical variable for this reaction—the absolute phase of fragment vibrations following the photodissociation.

We report a comprehensive study of the UV photolysis of I3 in ethanol solution, using femtosecond time resolved transient transmission experiments. We interpret our results to indicate that with high probability, photoexcitation leads to direct formation of di‐iodide ions within 300 fs, which are vibrating coherently. Through our experiments we have been able to determine that the time scales for vibrational dephasing, vibrational relaxation, and reorientation of the fragment ions are 400 fs, 4 ps, and 5 ps, respectively. Transmission signals at 620 nm and at 880 nm, which are above and below the λmax of the known absorption of I2, oscillate at a precisely opposite phase. This and other results presented indicate that through the oscillations we are observing coherent vibration of the I2 photofragment. UV transient transmission experiments have been conducted in order to characterize the time scales for recombination. Preliminary results show that recombination takes place on several time scales. A fast component is assigned to primary recombination, followed by vibrational relaxation on the ground state of I3. The impulsive nature of the I3 photoexcitation induces coherent symmetric stretching vibration in the ground state tri‐iodide population. Finally, the large number of dynamical variables probed directly allows us to record the chronology of this reaction with unprecedented detail. We directly observe a new and potentially informative dynamical variable for this reaction—the absolute phase of fragment vibrations following the photodissociation.

1992
Amir Waldman, Uri Banin, Eran Rabani, and Sanford Ruhman. 1992. “Temperature dependence of light scattering from neat benzene with femtosecond pulses: are we seeing molecules librate?” The Journal of Physical Chemistry, 96, 26, Pp. 10842-10848. Publisher's Version