AUTHOR=Hasegawa Hiroka , Walmsley Tiffany , Matsuda Akitaka , Morishita Toru , Madsen Lars Bojer , Jensen Frank , Tolstikhin Oleg I. , Hishikawa Akiyoshi 

TITLE=Asymmetric Dissociative Tunneling Ionization of Tetrafluoromethane in ω − 2ω Intense Laser Fields

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 10 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2022.857863

DOI=10.3389/fchem.2022.857863

ISSN=2296-2646

ABSTRACT=Dissociative ionization of tetrafluoromethane (CF_4) in linearly polarized  ω-2ω ultrashort intense laser fields (1.4\times10^{14} W/cm^2, 800 nm and 400 nm) has been investigated by three-dimensional momentum ion imaging. 
The spatial distribution of CF_^+ produced by CF_4 -> CF_3^+ + F + e^- exhibited a clear asymmetry with respect to the laser polarization direction. 
The degree of the asymmetry varies by the relative phase of the \omega and 2$\omega$ laser fields, showing that (i) the breaking of the four equivalent C-F bonds can be manipulated by the  laser pulse shape and that (ii) the C-F bond directed along the larger amplitude side of the \omega-2\omega electric fields tends to be broken in the dissociative ionization. 
Weak-field asymptotic theory (WFAT) shows that the tunneling ionization from the 4t_2 second highest-occupied molecular orbital (HOMO-1) surpasses that from the 1t_1 HOMO.
This predicts the enhancement of the tunneling ionization with electric fields pointing from F to C, in the direction opposite to that observed for the asymmetric fragment ejection.
Possible mechanisms involved in the asymmetric dissociative ionization, such as the post-ionization interactions, are discussed.