  In this paper we report an in situ electrochemical Sum-/Difference Frequency
Generation (SFG/DFG) spectroscopy investigation of the adsorption of nitrile
and CN -- from the ionic liquid 1-butyl-1-methyl-pyrrolidinium
bis(trifluoromethylsulfonyl) amide ([BMP][TFSA]) containing
4-{2-[1-(2-cyanoethyl)-1,2,3,4-tetrahydroquinolin-6-yl]-diazenyl}benzonitrile
(CTDB) at Au electrodes in the absence and in the presence of the
Au-electrodeposition process from K[Au(CN)$_2$ ]. The adsorption of nitrile and
its coadsorption with CN -- resulting either from the cathodic decomposition of
the dye or from ligand release from the Au(I) cyanocomplex yield
potential-dependent single or double SFG bands in the range 2,125-2,140
cm$^{-1}$, exhibiting Stark tuning values of ca. 3 and 1 cm$^{-1}$ V$^{-1}$ in
the absence and presence of electrodeposition, respectively. The low Stark
tuning found during electrodeposition correlates with the cathodic inhibiting
effect of CTDB, giving rise to its levelling properties. The essential
insensitivity of the other DFG parameters to the electrodeposition process is
due to the growth of smooth Au.
