UV and IR spectroscopy of cold 1,2-dimethoxybenzene complexes with alkali metal ions

作者：Inokuchi Yoshiya^*; Boyarkin Oleg V; Ebata Takayuki; Rizzo Thomas R

来源：Physical Chemistry Chemical Physics, 2012, 14(13): 4457-4462.

DOI：10.1039/c2cp24018a

We report UV photodissociation (UVPD) and IR-UV double-resonance spectra of 1,2-dimethoxybenzene (DMB) complexes with alkali metal ions, M+center dot DMB (M = Li, Na, K, Rb, and Cs), in a cold, 22-pole ion trap. The UVPD spectrum of the Li+ complex shows a strong origin band. For the K+center dot DMB, Rb+center dot DMB, and Cs+center dot DMB complexes, the origin band is very weak and low-frequency progressions are much more extensive than that of the Li+ ion. In the case of the Na+center dot DMB complex, spectral features are similar to those of the K+, Rb+, and Cs+ complexes, but vibronic bands are not resolved. Geometry optimization with density functional theory indicates that the metal ions are bonded to the oxygen atoms in all the M+center dot DMB complexes. For the Li+ complex in the S-0 state, the Li+ ion is located in the same plane as the benzene ring, while the Na+, K+, Rb+, and Cs+ ions are located off the plane. In the S-1 state, the Li+ complex has a structure similar to that in the S-0 state, providing the strong origin band in the UV spectrum. In contrast, the other complexes show a large structural change in the out-of-plane direction upon S-1-S-0 excitation, which results in the extensive low-frequency progressions in the UVPD spectra. For the Na+center dot DMB complex, fast charge transfer occurs from Na+ to DMB after the UV excitation, making the bandwidth of the UVPD spectrum much broader than that of the other complexes and producing the photofragment DMB+ ion.

• 出版日期2012