Abstract
The computation of Franck-Condon factors plays a key role for unraveling vibronic spectra and nonradiative process of molecules. In this work the photoelectron spectra of C122 were predicted by computing Franck-Condon factors. The equilibrium geometries and harmonic vibrational frequencies of five allotropes of C60C2C60 with dumbbell structures, including their cations and anions, were calculated at the B3LYP/6-31G(d) level. To facilitate the computation of Franck-Condon factors, a prescreening process for selecting transitions with stronger intensities was developed. The efficiency was further improved by rearranging the order of normal mode as the larger the maximum vibrational quantum number, the higher the order. The photoelectron spectra of C122- → C122 + e- and C122 → C122+ + e- were simulated. The simulated spectra are distinct for each molecule, indicating that the five allotropes of C122 can be identified by the experiment of photoelectron spectroscopy.
Highlights
In an ion mobility experiment, Shvartsburg et al observed that a lot of carbon clusters were formed upon laser desorption of C60/C70 films.1 The drift time distributions (DTD) for mass-selected cluster ions were structured, indicating the existence of allotropes with different geometries
For C122- and C122+, four types of ionic structures were proposed: a single-shell fullerene, a [2 + 2] cycloadduct attached with a C2 tail, a ball-and-chain dimer, and a sandwich dimer
The assignment of ionic structures based on the comparison between the experimental and calculated ion mobility is suffered from the difficulty of describing the interaction between the ion and the buffer gas accurately
Summary
In an ion mobility experiment, Shvartsburg et al observed that a lot of carbon clusters were formed upon laser desorption of C60/C70 films. The drift time distributions (DTD) for mass-selected cluster ions were structured, indicating the existence of allotropes with different geometries. The drift time distributions (DTD) for mass-selected cluster ions were structured, indicating the existence of allotropes with different geometries. The peaks present in the DTD were interpreted based on the relationship between the ion mobility and collision cross section. The cross section of collisions between the buffer gas (He) and the ions were obtained from classical trajectory calculations. The assignment of ionic structures based on the comparison between the experimental and calculated ion mobility is suffered from the difficulty of describing the interaction between the ion and the buffer gas accurately. The quantum nature of molecular interactions is not taken into account by trajectory calculations based on classical mechanics. Spectroscopic measurements usually provide richer and stronger evidence for identifying molecular structures, compared with the sole observable of ion mobility. This study aimed to answer the question: Can the structures of different C122 allotropes be identified using the technique of photoelectron spectroscopy?
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