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=10

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=<p>Dissociative ionization of tetrafluoromethane (CF<sub>4</sub>) in linearly polarized <italic>ω</italic>-2<italic>ω</italic> ultrashort intense laser fields (1.4 × 10<sup>14</sup> W/cm<sup>2</sup>, 800 and 400 nm) has been investigated by three-dimensional momentum ion imaging. The spatial distribution of <inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> produced by CF<sub>4</sub> → <inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mi mathvariant="normal">C</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> + F + e<sup>−</sup> exhibited a clear asymmetry with respect to the laser polarization direction. The degree of the asymmetry varies by the relative phase of the <italic>ω</italic> and 2<italic>ω</italic> laser fields, showing that 1) the breaking of the four equivalent C-F bonds can be manipulated by the laser pulse shape and 2) the C-F bond directed along the larger amplitude side of the <italic>ω</italic>-2<italic>ω</italic> electric fields tends to be broken. Weak-field asymptotic theory (WFAT) shows that the tunneling ionization from the 4<italic>t</italic><sub>2</sub> second highest-occupied molecular orbital (HOMO-1) surpasses that from the 1<italic>t</italic><sub>1</sub> 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 post-ionization interactions, are discussed.</p>