We ascribe the next, less intense, observed transitionpeak B at 286.2 eV-to an electronic transition from the 1sC* orbital (4a1) to π*. Hitchcock et al. also assigned this peak to a 1sC*→π* transition and concluded that the energy shift between peak A and B occurs primarily due to the chemical shift (of about 1.1 eV stronger binding) of the 1sC* orbital relative to the 1sC orbitals, while the energy of the π* orbital is insensitive to bromine substitution. Similar behavior was observed in chlorobenzene (ClBz), iodobenzene (IBz), and fluorobenzene (FBz). The influence of the halogen substitution on the 1s orbital of the nearest carbon atom (C*) has been explored in several other studies. For instance, by replacing the number of F atoms with hydrogens, Hitchcock et al. and Plashkevych et al. showed that the relative intensities of 1sC→π* and 1sC*→π* transitions are affected by the relative number of C and C* carbon sites. Interestingly, the position of the 1sC→π* and 1sC*→π* transitions was almost not affected by the change in the number of F atoms, indicating the localized behavior of the 1sC and 1sC* orbitals and that the energy of the π* orbital is unaffected by the substitution. In addition, it was proposed that a 1sC→3s transition contributes to the intensity of the peak assigned to the 1sC*→π* transition. Similarly, 1sC→π* and 1sC*→π* transitions are reported in the xray spectrum of C3H2Br to have similar amplitude ratio, emphasizing the dependence of the peak intensities on the number of core sites and the localized behavior near the C*-Br bond. Our computed 1sC*→π* transition energy matches well the experimental result, aside from a slightly larger separation between peak A and B, as can be seen from Figure (a) and (b). Next, peak C in Figure (a), observed to be at around 287 eV. The calculation suggest that this peak related to 1sC*→σ*(C*-Br) transition labeled as 6 in Figure (b), with a good agreement to previous results. The other transitions have previously been described as 1sC→5p (288.0 eV), 1sC→4d and 1sC→6s (289.0 eV), corresponding to peaks D, and E as shown in Table , and to sticks 7, 8 from our calculation. The binding energy reported from previous works to be 290.5 and 291.3 eV from 1sC and 1sC*, respectively. The black line in Figure (d) shows the absorption spectrum of BrBz + . The spectrum is obtained from ∆A = 𝑙𝑜𝑔(𝐼without UV / 𝐼with UV), where 𝐼without UV and 𝐼with UV are the transmitted signal of the x-ray flux without UV and with UV, respectively, after adding back 20% of neutral spectrum. The UV pulses at 267 nm ionize the molecule by resonance enhanced two-photon ionization (1+1 REMPI) after being focused with a 45 cm f.l. lens where the UV pulse energy is 25 μJ. The broadband HHG pulse near the carbon K-edge probes the prepared BrBz + after 1 ps time delay. Two-photon 267 nm excitation is in resonance with the first ionized state (EIon=8.992 eV), in which one electron is removed from the π orbital, creating a hole in the highest π(6b2) orbital. Consequently, the lowest-energy transition (at 281 eV) in the cation from a core orbital is of 1sC→π character, while a second transition (of 1sC*→π character) is expected to be 1 eV higher in energy. Evidence of these two transitions is just discernible in the experimental spectrum. The core-to-SOMO (singly occupied MO) 1sC→π transition in Bz + was found to be relatively weak in our previous study, and it is expected to be even weaker in BrBz + because the intensity is redistributed between two transitions from 1sC and 1sC* orbitals, in addition to possibly a more diffuse vibrational structure due to higher available energy (Eav) after ionization (Eph -EIon = Eav = 0.25 eV compared to 0.07 eV in Bz + ). Indeed, theory shows the presence of two major transitions from 1sC, namely 1sC(7a1)→π(6b2), 1sC(5a1)→π(6b2), in addition to the 1sC*(4a1)→π(6b2) transition at higher energy (blue sticks labelled 1, 2 and 3 in Figure (e) and in Table ). The next two peaks of nearly equal intensity, toward higher energy, a doublet peak structure, are labeled as G1 and G2, at 283.9 and 284.55 eV (0.65 eV difference) and are readily seen in the raw data inset in Figure (c) for BrBz + even before adding back 20% of the neutral benzene spectrum. These peaks are red-shifted compared to peak A (1sC→π*) of BrBz, and it is therefore reasonable to assign them to 1sC→π* transitions, similar to the previously reported Bz + spectrum. 9 Indeed, the transitions from 1sC to the lowest π* orbital observed in the x-ray spectrum of neutral Bz and of BrBz are remarkably similar and the energy of the π* orbital is not affected by replacing halogen atoms as pointed out above; the same is expected to occur in the x-ray spectrum of the cations. The doublet peak structure of G1 and G2 can be (partly) explained by the spin coupling of the three unpaired electrons, as recently observed in N2 + , CO + , and in Bz + . The splitting of the main peak in Bz + is more than 1 eV, caused mostly by spin coupling between unpaired electrons in 1sC, π and π* orbitals as substantiated by the calculations. The theoretical results have shown that Jahn-Teller (JT) shifts for Bz + cause a much smaller splitting of the two degenerate π* orbitals. Here, we attribute the observed doublet peak structure of BrBz + to a similar spin coupling effect. The calculations revealed the presence of two transitions from two different 1sC orbitals to π* (sticks 4 and 5 in Figure (e) and corresponding assignments in Table ), followed by a transition 1sC(7a1)→π*(3a2) (stick 6) plus two transitions, labeled as sticks 7 and 8, involving the same orbitals as sticks 4,5 but with different spin of the unpaired electron in the π orbital (SOMO). The next peak, labeled as H, fits well to the calculated 1sC→σ*(C*-Br) transition (labelled as stick 9), with an additional contribution from a 1sC*→π* transition (stick 10). This behavior is quite similar to the neutral BrBz, while in BrBz + the calculations show a more dominant influence of the transition to the σ*(C*-Br) orbital. The next dominant transitions in the experimental spectrum are labeled as peaks J1 and J2, at 288.2 and 288.60 eV. In the previously reported x-ray spectrum of Bz + , we did not observe major peaks in this energy region and, therefore, we consider these transitions as strongly related to the bromine atom.