Effect of Noncovalent Interactions on Conformers of the n-Butylbenzene Monomer Studied by Mass Analyzed Threshold Ionization Spectroscopy and Basis-set Convergent ab initio Computations

Abstract

Two conformational isomers of the aromatic hydrocarbon n-butylbenzene have been studied using two-color MATI (mass analyzed threshold ionization) spectroscopy to explore the effect of conformation on ionization dynamics. Cationic states of g auche-conformer III and anti- conformers IV were selectively produced by two-color excitation via the respective S 1 origins. Adiabatic ionization potentials of the gauche- and anti-conformations were determined to be 70146 and 69872 +/- 5 cm (-1) respectively. Spectral features and vibrational modes are interpreted with the aid of MP2/cc-pVDZ ab initio calculations, and ionization-induced changes in the molecular conformations are discussed. Complete basis set (CBS) ab initio studies at MP2 level reveal reliable energetics for all four n-butylbenzene conformers observed in earlier two-color REMPI (resonance enhanced multiphoton ionization) spectra. For the S 0 state, the energies of conformer III, IV and V are above conformer I by 130, 289, 73 cm (-1), respectively. Furthermore, the combination of the CBS calculations with the measured REMPI, MATI spectra allowed the determination of the energetics of all four conformers in the S 1 and D 0 states.

Rotamers of m-chloroanisole studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy

“…These methods can provide information about the active vibrations of rotamers in the electronically excited state. If the zero-kinetic energy (ZEKE) photoelectron [16][17][18] or mass-analyzed threshold ionization (MATI) [19][20][21][22][23] method couples with the resonant excitation scheme, it can provide information about the precise adiabatic IEs and active cation vibrations of the selected rotamers. Particularly, the MATI method has mass information and is suitable for studies of radicals, complexes, clusters, and isotopologues.…”

The shape of gaseous n‐butylbenzene: Assessment of computational methods and comparison with experiments

“…High resolution REMPI spectra and simulation based on MP2/cc-pVDZ computed rotational constants 20 allow to confirm the assignment of band A to conformer III and band D to conformer I (note that the conformer denomination in refs. [18][19][20][21] is different from that originally used by Simons and coworkers in refs. 15 and 16 ).…”

“…Weaker transitions are attributed to conformer IV but no signal seems to correspond to conformer V. Owing to signal intensities, it is suggested that the relative population of conformers I-IV would be equal to 20/2.5/2.5/1. Conformers of butylbenzene have been also studied using resonance enhanced multiphoton ionization (REMPI), mass analyzed threshold ionization (MATI) and zero electron kinetic energy (ZEKE) spectroscopy 18,19,21 completed by quantum chemistry computations. 20,21 In their first experimental studies, Müller-Dethlefs and coworkers 18,19 examined the two colors REMPI spectrum of butylbenzene and found it clearly comparable to the LIF spectrum reported by Simons and coworkers 15 in 1997.…”

“…18,19,21 Resonance enhanced multiphoton ionization and mass analyzed threshold ionization allow Müller-Dethlefs and coworkers 18,21 to accurately determine the adiabatic ionization energies of conformers I-IV. The values are 8.6733, 8.6630, 8.6972, and 8.6970 eV 6 0.0006 eV, respectively.…”

Ionization energy and active cation vibrations of trans -2-fluorostyrene

“…To the best of knowledge, neither the ionization energy (IE) nor the cation spectrum of trans-2-fluorostyrene has been reported. Both zero-kinetic energy (ZEKE) photoelectron [6][7][8] and mass-analyzed threshold ionization (MATI) [9][10][11][12] spectroscopy are powerful methods for recording the vibrationally resolved cation spectra. These experimental results give information about the precise adiabatic IE and active molecular vibrations in the cationic ground D 0 state.…”