Weak-Field Coherent Control of Photodissociation in Polyatomic Molecules

1. Weak-Field Coherent Control of Photodissociation in Polyatomic Molecules Alberto García-Vela Instituto de Física Fundamental Consejo Superior de Investigaciones Científicas Serrano, 123, 28006 Madrid, Spain I Workshop on Nonrigid Molecules in Atmospherical and Astronomical Environments, Huelva, 2019

2. Motivation • Control of the asymptotic photofragment state distributions • Successfully achieved in the strong-field regime • A challenging task under weak-field, one-photon conditions • Performance of the control scheme is illustrated by applying it to: • Vibrational predissociation of Br2(B,v’)-Ne • Photodissociation of CH3I in the A band The basis of the control scheme was reported earlier (H. Stapelfeldt and co., Phys. Rev. Lett. 89, 133004 (2002); G. Gerber and co., Phys. Rev. Lett. 89, 173001 (2002); S.A. Rice and co., Phys. Rev. Lett. 91, 243003 (2003)) • Previously applied to atomic and diatomic systems in order to modify • the superposition of initial states prepared with a laser field • But the present work is the first time which is applied to control • the product fragment distributions in polyatomic molecules

3. Foundations of control of asymptotic fragment distributions using two pulses delayed in time Interference term that modulates the spectral bandwith profile of the field Δt=t2-t1

4. Excitation of Br2(B,v’)-Ne Figure taken from K.C. Janda and co-workers, JCP 123, 054311 (2005)

5. Control of asymptotic fragment distributions of Br2-Ne(B,v’) using two pulses delayed in time • Spectral overlap  interference modulates spectral profile • Control over the asymptotic vibrational population is possible A. García-Vela,Phys. Chem. Chem. Phys. 18, 10346 (2016) A. García-Vela, J. Chem. Phys. 144, 141102 (2016) (Communication)

6. A-band CH3I photodissociation control CH3I photodissociation in the A band Varying Δt allows one to change the relative population of the three excited electronic state of the A band Interference between the two pulses provides a flexible way to modulate excitation to the different electronic states A. Serrano-Jiménez, L. Bañares, and A. García-Vela, Phys. Chem. Chem. Phys. 21, 7885 (2019)

7. Control of the CH3I photodissociation outcome Substantial modifications are achieved for both the I*/I branching ratio (by nearly a factor of two) and the anisotropy parameter β of the I channel (from -0.4 to 0.3) The presence of the conical intersection between the 3Q0 and 1Q1 states plays an important role in the control achieved A. Serrano-Jiménez, L. Bañares, and A. García-Vela, Phys. Chem. Chem. Phys. 21 7885 (2019)

8. Conclusions • It is possible to modify extensively the asymptotic fragment state distribution of a polyatomic molecule in the weak-field regime by applying a simple laser field consisting of two spectrally overlapping pulses delayed in time • The control scheme is flexible and of wide applicability to diferent molecular photodissociation processes

9. ACKNOWLEDGMENTS Alfredo Serrano-Jiménez, Instituto de Física Fundamental, CSIC, Spain Prof. Luis Bañares, U. Complutense de Madrid, Spain Projects from MINECO (Spain): CTQ2015-65033-P Finis Terrae, Centro de Supercomputación de Galicia, CESGA (Spain) MareNostrum, Barcelona Supercomputing Center-Red Española de Supercomputación, BSC-RES (Spain) and, … thank you for your attention!