Abstract
We investigate the photodissociation of helium-solvated cesium dimer cations using action spectroscopy and quantum chemical calculations. The spectrum of Cs2He+ shows three distinct absorption bands into both bound and dissociative states. Upon solvation with further helium atoms, considerable shifts of the absorption bands are observed, exceeding 0.1 eV (850 cm−1) already for Cs2He10 +, along with significant broadening. The shifts are highly sensitive to the character of the excited state. Our calculations show that helium atoms adsorb on the ends of Cs2 +. The shifts are particularly pronounced if the excited state orbitals extend to the area occupied by the helium atoms. In this case, Pauli repulsion leads to a deformation of the excited state orbitals, resulting in the observed blue shift of the transition. Since the position of the weakly bound helium atoms is ill defined, Pauli repulsion also explains the broadening.
Highlights
Resolved electronic spectroscopy in combination with theoretical calculations is a powerful technique to determine details of the geometrical arrangement and electronic structure of molecules or clusters
To obtain a quantum chemical description of the optical spectra, ground state structures of Cs2He+n ions were first modelled at the coupled cluster singles doubles (CCSD) level with the def2QZVP basis set on Cs and def2TZVP on He
To validate the theory as much as possible, excited states were modelled on various theory levels: time-dependent density functional theory (TDDFT) with the CAM-B3LYP functional; equation of motion – CCSD (EOMCCSD); multi-reference configuration interaction (MRCI) with an active space of one electron in 5 or 17 orbitals, MRCI(1,5) and MRCI(1,17), respectively; def2QZVPPD basis set was used on all atoms for excited state calculations
Summary
Resolved electronic spectroscopy in combination with theoretical calculations is a powerful technique to determine details of the geometrical arrangement and electronic structure of molecules or clusters. The quality of vibrationally resolved spectra depends critically on the temperature, as recently demonstrated for the assignment of the structure of Au4+.1 This has triggered the development of several cryogenic techniques, i.e., molecular beams,[2,3] matrix isolation,[4,5] helium droplets,[6,7] cryogenic traps[8,9,10,11,12,13,14,15,16,17,18,19,20] and cryogenic storage rings.[21,22,23,24,25] The low density of ionic targets requires special techniques, such as cavity ring down[26] or action spectroscopy.[27,28] Tagging of ions with a weakly bound messenger turns out to be suitable to measure absorption lines of ions, albeit leading to a matrix shift.[10,29] The binding energy of helium to ions is lower than for any other atom or molecule, leading to a minimum matrix shift.[30].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
