120th General Meeting of the KCS

Type Oral Presentation
Area Oral Presentation for Young Scholars in Physical Chemistry
Room No. Room 208+209+210
Time THU 10:15-:
Code PHYS.O-7
Subject Conformer-specifinc vibrational spectroscopy of molecular cations by high-resolution VUV-MATI technique
Authors Yu Ran Lee, Hong Lae Kim, Chan Ho Kwon*
Department of Chemistry, Kangwon National University, Korea
Abstract We have developed the high-resolution vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectrometer. Basically, key ideas on construction of the spectrometer with high-performance was a new ion source assembly consisting of a separate pulse field ionization (PFI) stage to improve the spectral resolution in the VUV-MATI spectrum and a dual stage extraction to achieve the first-order focusing of the MATI ions generated initially with the spatial distribution. This concept on instrumentation could be rationalized by utilizing the SIMION program (3D 7.0w, Win NT) which is used to calculate trajectories of charged particles by electric potentials for various configuration of the electrodes with the voltage. Thereafter, the ion source assembly was optimized at a specific configuration with four electrode plates. In the new ion source, the one stage is for applying a low PFI voltage and the other is for achieving the first-order space focusing of the MATI ions generated. This simple modification in the electrode assembly and the pulsing scheme allowed to enhance simultaneously the spectral resolution (∼ 8 cm-1) and strength of the MATI signal. In addition, the stability of the vacuum ultraviolet radiation generated by four wave difference frequency mixing in Kr was tremendously enhanced by increasing the volume of the Kr cell and effectively evacuating it. The excellent performance of the constructed VUV-MATI spectrometer has been ensured elucidating complicated vibrational structures of the pyridine cation and the 2-fluoropyridine cation. We also determined the accurate ionization energies and conformational structures of saturated heterocyclic molecules such as thietane, tetrahydro- thiophene, and aldehydes such as isobutanal, which play an important role in biological systems and interstellar media. Vibrational assignments of the observed VUV-MATI spectra could almost completely be achieved by simulating with the Franck-Condon factors and vibrational frequencies calculated adjusting geometrical parameters of the cationic conformers with the DFT method.
E-mail tyorange@hanmail.net