Electronic states and spectroscopic parameters of the iodocarbyne cation, CI+

Threshold Photoelectron Spectroscopy of the CH2I, CHI, and CI Radicals

“…Indeed, calculations place the value of the vertical transition at (v, v + ) = (0, 1), and using the experimental vertical transition (the most intense band at 8.45 eV) as a reference to match the simulated spectrum (see Figure 6 b) yields a very good agreement for the high energy part between 8.4 and 8.8 eV. From the bands within this interval, we obtain an experimental vibrational frequency of 760 ± 60 cm –1 for the ground state of CI + , in agreement with the calculated value of 810 cm –1 (ref ( 33 )) within our error bars and noticeably larger than the value of 630 cm –1 calculated for the neutral X 1 Σ + ground state. 31 This difference in the C–I stretching frequency for the cation and neutral ground state was also observed in the CH 2 I radical, as discussed previously, and in other diatomic species such as IO, where the vibrational frequency goes from 682 cm –1 in the neutral ground state to 810 cm –1 in the cation ground state, as the I–O bond length shortens.…”

“…Only photon energies below 9.5 eV are plotted due to the low signal-to-noise ratio above this value. The red sticks have been taken from the 300 K simulation reported by de Melo et al 33 and shifted by +6 meV with respect to their calculated ionization energy of 8.347 eV obtained at the RCCSD(T) level.…”

“…The corresponding TPES, depicted in Figure 6 b, shows a marked vibrational progression. de Melo et al 33 recently reported a theoretical study of the direct ionization of CI. They calculated adiabatic energies of 8.287 and 8.347 eV at the CASSCF/MRCI and RCCSD(T) levels of theory, respectively.…”

“…They calculated adiabatic energies of 8.287 and 8.347 eV at the CASSCF/MRCI and RCCSD(T) levels of theory, respectively. They also performed a Franck–Condon simulation for transitions to the X 1 Σ + ground cationic state and observed a vibrational progression reflecting the shortening of the bond distance from neutral (2.037 Å 31 ) to cation (1.926 Å 33 ). However, the imperfect agreement between simulated and experimental spectra, coupled to the low signal-to-background and the potential presence of autoionizations affecting the relative branch ratios, makes assignment of the adiabatic value challenging.…”

“… 26 , 29 − 32 The potential energy curves characterizing the ground and first excited states of the cation CI + were recently calculated and adiabatic ionization energies of 8.287 and 8.347 eV were obtained depending on the level of theory. 33 To the best of our knowledge, this is the only report regarding the cation CI + structure and the ionization energies. The cations CHI + and CI + have not been further considered and the adiabatic ionization energies have not been experimentally determined.…”