The possibility of using femtosecond IR spectroscopy to determine the composition of molecules in the gas phase

The possibility of using one method of femtosecond laser spectroscopy, IR pump-probe, is considered for analyzing the molecular composition of gas. The measured intramolecular relaxation time of the vibrational energy is proposed as an individual characteristic of molecules. A number of compounds of different classes having the molecular chromophore group C=O are investigated. It is shown that the characteristic relaxation times of the corresponding analytical signals in the resonant exciting of C=O vibrations are significantly different for different molecules (ten or more), making it possible to identify molecules in mixtures by means of temporal selection. The linear dependence of the analytical signal on the vapor pressure of the investigated compounds and the energy fluence of the exciting radiation is revealed. It is shown that the analytical signal is not dependent on the pressure of the buffer gas (nitrogen) up to 1 atm.