Ionization spectroscopy of conformational isomers of propanal: the origin of the conformational preference.
Two different conformational isomers of propanal, cis and gauche, are investigated by the vacuum-UV mass-analyzed threshold ionization (VUV-MATI) spectroscopy to give accurate adiabatic ionization potentials of 9.9997 +/- 0.0006 eV and 9.9516 +/- 0.0006 eV, respectively. cis-Propanal, which is the more stable conformer in the neutral state, becomes less stable in the cation compared to gauche-propanal. Vibrational structures revealed in the MATI spectra indicate that cis and gauche isomers undergo their unique structural changes upon ionization. The ionization of gauche-propanal induces a geometrical change along the conformational coordinate, suggesting that the steric effect in the ground state is diminished upon ionization. Natural bonding orbital (NBO) calculations provide the extent of hyperconjugation in each conformational isomer of propanal.
Choi
Sunyoung
S
Department of Chemistry and School of Molecular Science (BK21), KAIST, Daejeon (301-750), Republic of Korea.
Kang
Tae Yeon
TY
Choi
Kyo-Won
KW
Han
Songhee
S
Ahn
Doo-Sik
DS
Baek
Sun Jong
SJ
Kim
Sang Kyu
SK