Ultraviolet photodepletion spectroscopy of dibenzo-18-crown-6-ether complexes with alkali metal cations.
Ultraviolet photodepletion spectra of dibenzo-18-crown-6-ether complexes with alkali metal cations (M(+)-DB18C6, M = Cs, Rb, K, Na, and Li) were obtained in the gas phase using electrospray ionization quadrupole ion-trap reflectron time-of-flight mass spectrometry. The spectra exhibited a few distinct absorption bands in the wavenumber region of 35 450-37 800 cm(-1). The lowest-energy band was tentatively assigned to be the origin of the S(0)-S(1) transition, and the second band to a vibronic transition arising from the "benzene breathing" mode in conjunction with symmetric or asymmetric stretching vibration of the bonds between the metal cation and the oxygen atoms in DB18C6. The red shifts of the origin bands were observed in the spectra as the size of the metal cation in M(+)-DB18C6 increased from Li(+) to Cs(+). We suggested that these red shifts arose mainly from the decrease in the binding energies of larger-sized metal cations to DB18C6 at the electronic ground state. These size effects of the metal cations on the geometric and electronic structures, and the binding properties of the complexes at the S(0) and S(1) states were further elucidated by theoretical calculations using density functional and time-dependent density functional theories.
Choi
Chang Min
CM
Department of Chemistry, Chungbuk National University, Chungbuk 361-763, Korea.
Kim
Hwan Jin
HJ
Lee
Jun Ho
JH
Shin
Won Jik
WJ
Yoon
Tae Oh
TO
Kim
Nam Joon
NJ
Heo
Jiyoung
J