Doubly vibrationally enhanced four wave mixing spectroscopy in an acetonitrile–magnesium perchlorate mixture

Doubly vibrationally enhanced (DOVE) four wave mixing (FWM) spectroscopy has been used to study the mixture of Mg(ClO4)2 and deuterated acetonitrile (CD3CN) which serves as a model for metal ion complexes. In the mixture, there are free acetonitrile species and coordinated Mg2+–CD3CN species both of which have corresponding vibrational features in the middle infrared region including CN stretch ν2 and CC stretch ν4. In the free species, there is a combination band ν2 + ν4 at 3092 cm−1. It is unclear whether there exists a combination band in the coordinated species of which the existence is important for implementing the DOVE-FWM. Here we have determined a combination band ν2 + ν4 at 3153 cm−1 for the coordinated species by using IR absorption spectroscopy and subsequently applied the DOVE-FWM to the mixture. The measured DOVE spectra show a strong DOVE enhancement not only for the free species but also for the coordinated species. The results demonstrate the feasibility of the DOVE-FWM methods for measuring the coordinated species involving charge transfer interaction, and provide a key feature for metal ion complex studies.