Site-specific tunnel-ionization in high harmonic generation in molecules

We demonstrate that the standard picture of strong-field tunnel-ionization from molecules should be reformulated. The extended nature of the molecular potential implies the separation of some of the molecular sites from the edge of the ionization barrier. We show that the dependence of the tunnel probability with the distance to the barrier is translated into the ionized wavepacket, modifying substantially the high-order harmonic emission. The introduction of the dependence of tunnel ionization with the molecular site significantly improves the theoretical description of high-order harmonic generation in molecules, which is used as a cornerstone in high-harmonic spectroscopy and attosecond imaging.C H-G and L P acknowledge support from Junta de Castilla y León and European Union, FEDER (Project SA287P18), Spanish MICINN (FIS2016-75652 P). C H-G acknowledges Ministerio de Ciencia, Innovación y Universidades for a Ramón y Cajal contract (RYC-2017-22745), co-funded by the European Social Fund. L R acknowledges support from Ministerio de Educación, Cultura y Deporte (FPU16/02591). A P acknowledges support from Comunidad de Madrid through the TALENTO program with Reference No. 2017-T1/IND-5432. We thankfully acknowledge the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (FI-2019-1-0013)