Electronic states of carbon disulphide in the 5.5-11.8 eV region by VUV photo absorption spectroscopy

- Photo absorption spectra of CS2 in the 5.5 to 11.8 eV region recorded using synchrotron radiation.
- Valence and Rydberg transitions assigned to singlet/triplet states originating from three HOMOs.
- TDDFT computations of vertical excited states reported for the first time.
- Ambiguity in assignment of low lying valence/Rydberg states clarified.
- Consolidated experimental and theoretical work in VUV region.

The photo absorption spectrum of carbon disulphide (CS2) is recorded using synchrotron radiation in the 5.5-11.8 eV region. The richly structured spectrum of CS2 consists of valence and Rydberg transitions up to the first ionization potential (IP) at ~10.1 eV and a few discrete peaks above the first IP. The low lying electronic states of CS2 are assigned to the singlet or triplet states originating from {2πg→3πu, 7σg, 8σg, 6σu, 4πu, 3πg, 9σg}, {2πu→3πu, 7σg} and {5σu→3πu} excitations. Rydberg series of type nlλ(l=s, p, d, f and λ=σ,π,δ,ϕ) are observed along with associated vibronic structure in a few low lying members. The derived quantum defect values for the s(~2.0), p(~1.6), d(~0.4) and f(~0.1) Rydberg states are consistent with excitation from sulphur non-bonding orbitals. The comprehensive experimental work presented here and the revisit of the study of electronic spectrum of CS2 gives a clearer picture of the nature and origin of various transitions and helps in interpreting several unassigned peaks. The vibrational features observed above the first IP are attributed to autoionization from a high lying Rydberg state. Theoretical calculations using the time dependent density functional theory method assists in evaluating vertical excitation energies, nature of the transitions and confirming or suggesting electronic assignments of a few low lying valence transitions where ambiguity existed.