Figure 1.

(a) The two-dimensional slice (P_y ≈ 0) through the three-dimensional momentum distribution obtained from VMI data of C₂D₃ ⁺ photofragments produced in the nω + C₂D₄ → C₂D₄ ⁺ → C₂D₃ ⁺  + D process. The laser polarization, indicated by the arrow, is vertical (0–180°) in all panels. The faint outer ring is mirrored in the D⁺ momentum image, suggesting that those ions are part of the double ionization process (D⁺  + C₂D₃ ⁺). The laser pulses are approximately 5 fs in duration with a central wavelength of 740 nm and a focused peak intensity (I_peak) of approximately 6 × 10¹⁴ W cm⁻². The corresponding focal-volume-averaged intensity, I_avg, (see the Methods section for details) is approximately 2 × 10¹³ W cm⁻². (b) Measured yield as a function of the relative angle between the C₂D₃ ⁺ photofragment and the laser polarization. The yield is obtained for the inner single ionization followed by hydrogen elimination process and excludes the faint outer double ionization process. (c) Calculated angular distribution for the C₂D₃ ⁺ photofragments (see Methods for details) without including FDRC orbitals at a uniform intensity of 9 × 10¹³ W cm⁻². (d) Similar calculations for an intensity of 9 × 10¹³ W cm⁻² but with the ionization from FDRC orbitals included. The ethylene HOMO has π symmetry.