Two-Color Zero Kinetic Energy Photoelectron Spectra of Benzonitrile and Its van der Waals Complexes with Argon. Adiabatic Ionization Potentials and Cation Vibrational Frequencies

Abstract

Benzonitrile and its van der Waals (vdW) complexes with argon (benzonitrile-Ar and benzonitrile-Ar 2 ) have been studied in supersonic jets by two-color zero-kinetic-energy (ZEKE) photoelectron spectroscopy for the first time. From the (1+1′) ZEKE photoelectron spectra obtained via the first electronic excited state (S 1 ), we have determined adiabatic ionization potentials as I a (benzonitrile) ) 78 490 ( 2 cm -1 (9.7315 ( 0.0002 eV), I a (benzonitrile-Ar) ) 78 241 ( 4 cm -1 (9.7007 ( 0.0005 eV), and I a (benzonitrile-Ar 2 ) ) 78 007 ( 4 cm -1 (9.6716 ( 0.0005 eV). These values indicate that the decrease in ionization potential due to the complex formation (∆I a ) -249 and -483 cm -1 , respectively) is very large compared with other monosubstituted benzenes. Eleven low-frequency vibrational modes of the bare benzonitrile cation below 1300 cm -1 have been identified in the ZEKE photoelectron spectra. The in-plane CsCtN bending mode (33 + ) and the out-of-plane C-C-C bending mode (22 + ) have been clearly identified from the ZEKE photoelectron spectra obtained via the S 1 vibrational levels 33 1 and 22 2 , respectively. Furthermore, in the benzonitrile-Ar and -Ar 2 spectra, we have observed well-resolved vibrational progressions with very low frequencies of 12 and 9 cm -1 , respectively, which may be assigned to the vdW bending mode (b x + ) and the vdW symmetric bending mode (b xs + ) along the substituent axis, respectively.

Mass analyzed threshold ionization spectra of phenol⋯Ar2: ionization energy and cation intermolecular vibrational frequencies

“…The structure of the progression with a spacing of 10 cm À1 observed in the MATI spectrum via the S 1 0 0 state of phenolÁ Á ÁAr 2 (2p) is similar to those seen in aniline + Á Á ÁAr 2 (2p), 7 benzonitrile + Á Á ÁAr 2 (2p), 3 and fluorobenzene + Á Á ÁAr 2 (2p). 4 The vibrational spacing was found to be 9 cm À1 for the case of benzonitrile and fluorobenzene, and 11 cm À1 for aniline.…”

“…7 These ratios are slightly larger than those observed for fluorobenzene and benzonitrile (12/9). 3,4 The b x and b x assignments for phenol + Á Á ÁAr n (np) with n = 1 and 2 can be further confirmed by considering the following simple model. 6 The reduced masses m b x and m b x for the vibrational modes b x and b x are given by eqn (1) and (2),…”

“…Interestingly, this value is slightly larger than the corresponding values obtained for isoelectronic aniline (+) Á Á ÁAr 2 (8.81) 7 , fluorobenzene (+) Á Á ÁAr 2 (61) 4 , and benzonitrile (+) Á Á ÁAr 2 (61). 3 At this stage, it is, however, rather difficult to extract more quantitative information about the actual changes in the potential energy surface in phenol (+) Á Á ÁAr 2 (2p) upon ionization due to the severe limitations of the employed harmonic one-dimensional model, which for example neglects the effects of anharmonicity and intermolecular mode mixing arising from Duschinsky rotation. Moreover, as the reaction coordinate for the p -H switching reaction is not completely established, 14,23 the current result provides only approximate information about the energetics of this isomerization process (e.g., the barrier height).…”

“…These techniques provide essential information of the intermolecular interaction potential, including structure and intermolecular vibrational frequencies. Previous examples of A (+) Á Á ÁAr n clusters with aromatic molecules include A = benzonitrile, 2,3 fluorobenzene, 4,5 and aniline. [6][7][8][9][10] Phenol is another fundamental mono-substituted benzene molecule with an electron donor group (OH) and two principle binding sites for neutral ligands.…”

Molecular and supramolecular chirality: R2PI spectroscopy as a tool for the gas‐phase recognition of chiral systems of biological interest

“…[107][108][109][110][111][112][113][114] Here, the most stable [1,1] isomer invariably predominates at the supersonic beam temperature. The two argon atoms interact with the aromatic ring in the same way as in the monosolvated [1,0] complex.…”