Decoding strong-field ionization of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">H</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> via photoelectron momentum torus

Strong-field ionization of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi mathvariant="normal">H</a:mi><a:mn>2</a:mn></a:msub></a:math> in circularly polarized laser fields (1035 nm, 35 fs, <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mo>∼</c:mo><c:mn>1</c:mn><c:mo>×</c:mo><c:msup><c:mn>10</c:mn><c:mn>14</c:mn></c:msup><c:mspace width="0.16em"/><c:mi mathvariant="normal">W</c:mi><c:mo>/</c:mo><c:msup><c:mrow><c:mi>cm</c:mi></c:mrow><c:mn>2</c:mn></c:msup></c:mrow></c:math>) has been studied by three-dimensional electron-ion coincidence momentum imaging. Both the effective ionization potential and the applied laser electric field amplitude are simultaneously determined from the parameters characterizing the tunnel-electron torus in momentum space, using the adiabatic theory of strong-field ionization extended to include higher-order nonadiabatic effects as a reference. The effective ionization potential of <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:msub><f:mi mathvariant="normal">H</f:mi><f:mn>2</f:mn></f:msub></f:math>, obtained with an accuracy and precision of <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:msup><h:mn>10</h:mn><h:mrow><h:mo>−</h:mo><h:mn>2</h:mn></h:mrow></h:msup></h:math> a.u., reveals a clear shift from the field-free value. Dependence on both the field amplitude and the ionization pathways to <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:msup><i:mrow><i:msub><i:mi mathvariant="normal">H</i:mi><i:mn>2</i:mn></i:msub></i:mrow><i:mo>+</i:mo></i:msup></i:math> and <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"><k:mrow><k:msup><k:mtext>H</k:mtext><k:mo>+</k:mo></k:msup><k:mo>+</k:mo><k:mtext>H</k:mtext></k:mrow></k:math> is also resolved. These findings demonstrate that the target-specific properties can be quantitatively decoded from the structure of the photoelectron momentum torus, thus establishing a basis for quantitative ultrafast tunnel-electron spectroscopy.