Hyun S. Yoo

Rotational spectroscopy of vibrationally excited states by infrared-Fourier transform microwave–microwave triple-resonance spectroscopy

A Fourier transform microwave (FTMW) spectroscopy-based technique for measuring the rotational spectrum of vibrational excited states is demonstrated. A pulsed infrared laser is used to prepare the excited state outside the FTMW cavity. Following laser excitation, the molecules drift into the FTMW cavity region. The FTMW spectrometer is used to monitor a single rotational transition in the excited state. The rotational spectrum of one of the states involved in the transition monitored by the FTMW spectrometer is obtained through the Autler–Townes splitting of the quantum state caused by the application of resonant microwave radiation to the cavity region.

Conformer-Specific Ionization Spectroscopy of Bromocyclohexane: Equatorial versus Axial Conformers

Ionization of equatorial and axial conformational isomers of the chair-bromocyclohexane is investigated with use of the vacuum ultraviolet mass-analyzed threshold ionization (MATI) spectroscopic technique. Two distinct ionization energies of 9.8308 ± 0.0025 and 9.8409 ± 0.0025 eV are determined for equatorial or axial conformers, respectively. From the conformer-selective vibrational analysis, it is found that the equatorial conformer undergoes a drastic structural change upon ionization especially along the C-Br distortion mode, whereas the axial conformer shows the modest change along the ring-puckering mode with ionization, corresponding to the reaction coordinate for the conformational interconversion. Density functional theory (DFT) calculations with and without considering the spin-orbit coupling provide the appropriate mode assignments for the vibrational bands active in the ionization spectra. Natural bond orbital (NBO) analysis is carried out to give insights into the contribution of the anomeric effect to the structure-energy relationship in each conformational isomer.