Publication Date:
2015-04-02
Description:
Identification of many Rydberg states in iodobenzene, especially from the first and fourth ionization energies (IE 1 and IE 4 , X 2 B 1 and C 2 B 1 ), has become possible using a new ultraviolet (UV) and vacuum-ultraviolet (VUV) absorption spectrum, in the region 29 000-87 000 cm −1 (3.60-10.79 eV), measured at room temperature with synchrotron radiation. A few Rydberg states based on IE 2 (A 2 A 2 ) were found, but those based on IE 3 (B 2 B 2 ) are undetectable. The almost complete absence of observable Rydberg states relating to IE 2 and IE 3 (A 2 A 2 and B 2 B 2 , respectively) is attributed to them being coupled to the near-continuum, high-energy region of Rydberg series converging on IE 1 . Theoretical studies of the UV and VUV spectra used both time-dependent density functional (TDDFT) and multi-reference multi-root doubles and singles-configuration interaction methods. The theoretical adiabatic excitation energies, and their corresponding vibrational profiles, gave a satisfactory interpretation of the experimental results. The calculation s indicate that the UV onset contains both 1 1 B 1 and 1 1 B 2 states with very low oscillator strength, while the 2 1 B 1 state was found to lie under the lowest ππ ∗ 1 1 A 1 state. All three of these 1 B 1 and 1 B 2 states are excitations into low-lying σ ∗ orbitals. The strongest VUV band near 7 eV contains two very strong ππ ∗ valence states, together with other weak contributors. The lowest Rydberg 4b 1 6s state (3 1 B 1 ) is very evident as a sharp multiplet near 6 eV; its position and vibrational structure are well reproduced by the TDDFT results.
Print ISSN:
0021-9606
Electronic ISSN:
1089-7690
Topics:
Chemistry and Pharmacology
,
Physics
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