Ultraviolet Photodepletion Spectroscopy of Dibenzo-18-Crown-6-Ether Complexes with Alkaline Earth Metal Divalent Cations

详细信息    查看全文

• 作者：Chang Min Choi ; Jun Ho Lee ; Yong Hun Choi ; Hwan Jin Kim ; Nam Joon Kim ; Jiyoung Heo
• 刊名：Journal of Physical Chemistry A
• 出版年：2010
• 出版时间：October 28, 2010
• 年：2010
• 卷：114
• 期：42
• 页码：11167-11174
• 全文大小：309K
• 年卷期：v.114,no.42(October 28, 2010)
• ISSN：1520-5215

文摘

Ultraviolet photodepletion spectra of dibenzo-18-crown-6-ether complexes with alkaline earth metal divalent cations (A²⁺−DB18C6, A = Ba, Sr, Ca, and Mg) were obtained in the gas phase using electrospray ionization quadrupole ion-trap reflectron time-of-flight mass spectrometry. Each spectrum exhibits the lowest energy absorption band in the wavenumber region of 35400−37800 cm⁻¹, which is tentatively assigned as the origin of the S₀−S₁ transition of A²⁺−DB18C6. This origin band shows a red shift as the size of the metal dication increases from Mg²⁺ to Ba²⁺. The binding energies of the metal dications to DB18C6 at the S₀ state were calculated at the lowest energy structures optimized by the density functional theory and employed with the experimental energies of the origin bands to estimate the binding energies at the S₁ state. We suggest that the red shifts of the origin bands arise from the decrease in the binding energies of the metal dications at the S₁ state by nearly constant ratios with respect to the binding energies at the S₀ state, which decrease with increasing size of the metal dication. This unique relationship of the binding energies between the S₀ and S₁ states gives rise to a linear correlation between the relative shift of the origin band of A²⁺−DB18C6 and the binding energy of the metal dication at the S₀ state. The size effects of the metal cations on the properties of metal−DB18C6 complex ions are also manifested in the linear plot of the relative shift of the origin band as a function of the size to charge ratio of the metal cations, where the shifts of the origin bands for all DB18C6 complexes with alkali and alkaline earth metal cations are fit to the same line.