12001-89-7Relevant academic research and scientific papers
Zero kinetic energy spectroscopy: Mass-analyzed threshold ionization spectra of chromium sandwich complexes with alkylbenzenes, (η6- RPh)2Cr (R = Me, Et, i-Pr, t-Bu)
Ketkov, Sergey Y.,Selzle, Heinrich L.,Cloke, F. Geoffrey N.,Markin, Gennady V.,Shevelev, Yury A.,Domrachev, Georgy A.,Schlag, Edward W.
, p. 11298 - 11303 (2010)
For over 25 years zero kinetic energy (ZEKE) spectroscopy has yielded a rich foundation of high-resolution results of molecular ions. This was based on the discovery in the late 60's of long-lived ion states throughout the ionization continuum of molecular ions. Here, an example is chosen from another fundamental system pioneered at this university. The mass-analyzed threshold ionization (MATI) spectra of jet-cooled chromium bisarene complexes (η6-RPh)2Cr (R = Me (1), Et (2), i-Pr (3), and t-Bu (4)) have been measured and interpreted on the basis of DFT calculations. The MATI spectra of complexes 1 and 2 appear to reveal features arising from ionizations of the isomers formed by the rotation of one arene ring relative to the other. The 1 and 2 MATI spectra show two intense peaks corresponding to the 000 ionizations with inverse intensity ratios. As indicated by the DFT calculations, the intensity ratio change on going from 1 to 2 results from different isomers contributing to each MATI peak. The ionization energies corresponding to the 000 peaks are 42746 ± 5 and 42809 ± 5 cm-1 for compound 1 and 42379 ± 5 and 42463 ± 5 cm-1 for complex 2. The 1 and 2 spectra show also the weaker features representing transitions to the vibrationally excited cationic levels, the signals of individual rotamers being detected and assigned on the basis of calculated vibrational frequencies. The MATI spectra of compounds 3 and 4 reveal only one strong peak because of close ionization potentials of the isomers contributing to the MATI signal. The 3 and 4 ionization energies are 42104 ± 5 and 41917 ± 5 cm-1, respectively. The precise values of ionization energies obtained from the MATI spectra reveal a nonlinear dependence of the IE on the number of Me groups in the alkyl substituents of (η6-RPh)2Cr. This can be explained by an increase in the molecular zero point energies on methylation of the substituents.
The electronic absorption spectra of the alkyl-substituted derivatives of bis(benzene)chromium(0) in the vapour phase
Domrachev, G. A.,Ketkov, S. Yu.,Razuvaev, G. A.
, p. 341 - 348 (1987)
The UV and visible absorption spectra of (arene)2chromium(0) (arene=benzene (I), toluene (II), ethylbenzene (III), cumene (IV), tert-butylbenzene (V), mesitylene (VI)) in the vapour phase have been invesigated.Four band systems A, B, C and D are revealed in the spectra.The bands of the system with the shortest wavelengths, D, represent the Rydberg series.The first ionisation potentials IPa1g of I-VI determined from the Rydberg band frequencies are 5.45, 5.29, 5.25, 5.21, 5.18 and 5.01 eV respectively.The Rydberg bands correspond to the allowed electrodipole transitions from the highest occupied moloecular orbital (MO) a1g to the vacant MO of either the a2u or e1u type.System C corresponds to the intense band of the solution spectra.The electronic transition e2g -> e*2u obviously makes a great contribution to this system.System B is assigned to the transition from a1g to vacant a2u or e1u MO, which can be Rydberg orbitals.System A can be assigned to the a1g -> e*2u transition or to the Rydberg transition, which is forbidden in the D6h point group but becomes allowed upon reduction of symmetry.
