Determination of highest occupied molecular orbital and cationic structures of cyclopentanone using high‐resolution vacuum ultraviolet mass‐analyzed threshold ionization mass spectrophotometry

Abstract

The conformational structure of cyclopentanone (CP) and the photoionization dynamics of the corresponding conformer were investigated using the high‐resolution vacuum ultraviolet mass‐analyzed threshold ionization (MATI) spectroscopic technique. To identify the conformer corresponding to the measured MATI spectrum, the potential energy surfaces associated with the twisting and carbonyl wagging motions in the S0 and D0 states were constructed at the B3LYP/cc‐pVTZ level, where the twisted conformer in both states corresponded to the global minimum. Furthermore, the Franck–Condon fitting indicated that the cationic conformer had a warped twisted C1 symmetry rather than C2 symmetry. This implies that the ionization‐induced ring distortion can be principally attributed to the removal of an electron from the highest occupied molecular orbital, which consists of the nonbonding orbital of the oxygen atom in the carbonyl group interacting with the σ orbitals in the ring of the twisted CP conformer.

Determination of the highest occupied molecular orbital and conformational structures of morpholine based on its conformer-specific photoionization dynamics

“…13 In addition, the uncertainty in the measured AIE value was considered statistically along with the total experimental error for VUV generation and the applied electric fields and spectral resolution, although the uncertainty estimated for this peak profile analysis was ∼1 cm −1 . 18,20,21…”

“…A tiny electric jitter generated after the falling of the high-voltage pulse was used to lengthen the lifetime of the high-n Rydberg states via m l mixing, leading to the production of the zero kinetic energy (ZEKE) states. 21,23 Subsequently, morpholine molecules in the ZEKE states just below the ionization threshold and converging to the cationic states were ionized and simultaneously accelerated into the delayedextraction stage by a PFI field of 3.5 V cm À1 applied after a delay of B15 ms from the VUV laser pulse. The arrived MATI ions were then extracted from the delayed-extraction stage for first-order space focusing, passed through a field-free region, and subjected to mass-selective detection using a dualmicrochannel plate at the end of the time-of-flight tube.…”

“…13 In addition, the uncertainty in the measured AIE value was considered statistically along with the total experimental error for VUV generation and the applied electric fields and spectral resolution, although the uncertainty estimated for this peak profile analysis was B1 cm À1 . 18,20,21 A conspicuous spectral feature in Fig. 1 is that the intensity of the 0-0 band in the VUV-MATI spectrum is the highest, implying that the geometrical changes that occur upon ionization do so in accordance with the FC principle for the adiabatic ionic transition between the S 0 and D 0 states.…”

“…It was previously demonstrated that high-resolution vacuum ultraviolet mass-analyzed threshold ionization (HR VUV-MATI) spectroscopy using a one-photon scheme is effective for exploring the conformational structures of polyatomic molecules as well as their conformer-specific photoionization dynamics and the inducing cationic structure of the conformers. [14][15][16][17][18][19][20][21] In particular, the conformational structures of tetrahydrofuran and tetrahydrothiophene, which are saturated five-membered heterocyclic molecules, were investigated using the constructed potential energy surfaces (PESs) associated with the conformational changes. 14 The replacement of the methylene group in cyclopentane with a heteroatom such as oxygen or sulfur changes the conformational structure, in contrast to the case for cyclopentane.…”

Conformational Structures of Neutral and Cationic Pivaldehyde Revealed by IR-Resonant VUV-MATI Mass Spectroscopy

“…In this study, we performed IR-resonant VUV-MATI spectroscopy using the home-built HR VUV-MATI mass spectrometer, and its details were provided in previous studies [ 23 , 24 , 31 , 39 ].…”