Libration induced stretching mode excitation for pump-probe spectroscopy in pure liquid water

A femtosecond pump-probe technique was proposed to study pure liquid water in the infrared and avoid thermal effects. The technique based on libration induced stretching excitation of water molecules, allows direct observation of resonant dipolar energy transfer in pure water. The infrared spectrum of water was dominated by a strong absorption between 3000 and 3600 cm ^-1 due to symmetric and antisymmetric stretching modes. The results show that the response of pure water to an environmental change is strongly influenced by ultrafast energy transfer, with a characteristic time of about 100 fs.