用和频振动光谱研究乙腈/金电极界面，观测到乙腈的甲基振动峰强度随施加的电极电势而变化.当电极电势越过零电荷电势（pzc）时，甲基振动峰符号发生反转，这意味着基团取向发生反转（flip-flop）.由此推断出乙腈分子在金电极界面的吸附构型.即在零电荷电势下，电极界面吸附的乙腈分子构型为甲基靠近电极表面而腈基远离电极表面；而高于零电荷电势则电极界面吸附的乙腈分子构型发生反转，变为腈基靠近电极表面而甲基远离电极表面的构型.

The electrochemical interface between liquid acetonitrile and polycrystal gold electrode is investigated by in situ infrared visible sum frequency generation spectroscopy (SFG-VS). The structure of acetonitrile adsorbed at polycrystal gold electrode surface is studied as a function of electrode potential. The SFG spectra of CH3 group indicate acetonitrile orients in response to the electrode potential. The SFG signal of CH3 group turns lower as the electrode potential changes from -700mV to 300mV, and vanishes around the 300mV(pzc), then becomes a negative signal above 500mV, which indicates that the orientation is predominately with the CH3 group toward the metal between -700 and 300mV and with the CN group toward the metal above 300 mV. It is the first time to observe the flip-flop behavior of acetonitrile dipole at the polycrystal gold electrode surface, from which we may infer that the flip-flop behavior of acetonitrile is a common phenomenon.