High-Resolution Mass-Analyzed Threshold Ionization Study of Deuterated Derivatives of Bis(η⁶-benzene)chromium

Abstract

Two-color multiphoton mass-analyzed threshold ionization (MATI) spectra of jet-cooled (η6-C6D6)2Cr and (η6-C6D5H)(η6-C6D6)Cr have been obtained for the first time with excitation of the sandwich molecules via vibronic components of the 3d z 2 → R4p x , y Rydberg transition. The ionization energies determined with extremely high accuracy (±0.0004 eV) on the basis of the MATI experiment are 5.4558 and 5.4562 eV, respectively. The simultaneous measurement of the two MATI spectra in one experiment reveals clearly the increase in the ionization energy caused by substitution of one deuterium atom in (η6-C6D6)2Cr with hydrogen. The MATI experiment demonstrates a nonlinear dependence of the ionization potential on the number of deuterium atoms in the bis(η6-benzene)chromium molecule. Deuteration appears to decrease both the ionization energy and the R4p x , y Rydberg term value. The decrease in the term value is a result of the Jahn−Teller instability of the R4p x , y Rydberg state. The ground-state cation vibrational frequencies of the totally symmetric valence metal−ligand stretch ν21 and CH umbrella vibration ν11as determined from the MATI spectra are, respectively, 249 ± 3 and 594 ± 3 cm-1 for (η6-C6D6)2Cr+ and 251 ± 3 and 595 ± 3 cm-1 for (η6-C6D5H)(η6-C6D6)Cr+. These values correspond to the free gas-phase cations.

Direct Detection of Individual Bis(arene) Rotational Isomers in the Gas Phase by Mass‐Analyzed Threshold Ionization Spectroscopy

“…calcd =278 cm −1 ). The corresponding peak is also revealed by the MATI spectra of [(η 6 ‐C 6 H 6 ) 2 Cr] 5c–e. The feature at 42 908 cm −1 (the separation from the IE is 182 cm −1 ) is associated with a totally symmetric vibration B, which represents the ring tilt with the C ring –C Me out‐of‐plane bend and the Me group torsion ($\bar \nu $ vibr.…”

“…Recently, fascinating insight into the bonding situation of bis(benzene) complexes has been provided by laser spectroscopic techniques 5. Unique, precise information concerning ionization energies (IEs), excited‐state properties, and vibrational frequencies of free (η 6 ‐C 6 H 6 ) 2 Cr molecules was obtained by resonance‐enhanced multiphoton ionization (REMPI),5a zero electron kinetic energy (ZEKE),5b and mass‐analyzed threshold ionization (MATI)5c–e methods. Substitution of hydrogen atoms in the benzene rings with various functional groups changes strongly the reactivity of sandwich systems, the properties of substituted molecules being dependent not only on the nature of the substituent but also on the conformational behavior.…”

“…Besides high‐resolution IE values, MATI spectra can provide precise information on cationic vibrational frequencies 5c–e. 14 Analysis of vibrational structures in the MATI spectra of 1 and 2 appears to give unambiguous evidence of the signals arising from distinct rotational isomers of the toluene complex.…”

Pulsed-field ionization spectroscopy of high Rydberg states (n=50–200) of bis(η6-benzene)chromium

“…The high-resolution MATI spectrum is taken to give the detailed vibrational structure of the Cr͑Bz͒ 2 cation. In this work, we greatly improved the spectral resolution of the MATI spectrum of Cr͑Bz͒ 2 compared with other previous works, 23,[26][27][28] resolving the earlier ambiguity in the vibrational mode assignment. Furthermore, our MATI spectrum provides many newly found vibrational frequencies which are essential for the understanding of the nature of the metal-benzene bonding.…”

“…Pulsed-field ionization ͑PFI͒ of high Rydberg states of atoms and molecules has been a hot topic especially in the late 1990s, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] since excellent spectroscopic tools such as zero-electron kinetic energy ͑ZEKE͒ or mass-analyzed threshold ionization ͑MATI͒ spectroscopy rely on the PFI of long-lived high n Rydberg states. [18][19][20][21][22][23][24][25][26][27][28] The mechanism of the enormous lifetime lengthening of high Rydberg states has been subjected to intensive investigation for many chemical systems. 1,2,29 Through a number of excellent experimental and theoretical studies, it is now well accepted that the lifetime lengthening is mainly due to the l mixing induced by a stray field which cannot be easily avoided in most laboratories.…”