Fig. 2: Coulomb explosion momentum-space images of 2-thiouracil without UV excitation.

The molecular coordinate frame is defined by the emission direction of the S atom providing the z axis. The y-z plane is spanned by the emission directions of the S⁺ and O⁺ ions. The x axis is perpendicular to the y-z plane. a “Top view” projection of the measured momentum-space data of the oxygen ions and the protons. b “Side view” projection of the measured proton momenta. The momenta have been normalized such that the magnitude of the sulfur momentum equals 1 for each molecular ionization event. c Angular emission distribution of the protons in the molecular frame indicated by the scheme at the left, which is defined by the difference and sum momenta of the S⁺ and O⁺ ions. In the given representation by the spherical coordinates Θ and Φ (right panel), H₁₁ and O appear at two positions as the Φ angle wraps around. H₁₀ and H₁₂ are located at the poles and thus extend across a wide range of Φ. For details see the main text.