Relaxation enhancement from intra- to intermolecular vibrations in water continuously excited by wavelength-selective infrared radiation

The relaxation from intra- to intermolecular vibrations of water is compared in the cases of the infrared heating that emits the radiation to the infrared absorption band of water with a wavelength-selective emitter and the conductive heating with a heater. The wavelength-selective emitters have a metamaterial structure of Au/Cr/Al2O3/Au/Cr/substrate and continuously emit the radiation in the wavelength range about 3.03 or 6.06 μm, corresponding to the stretching or bending vibrations of water, respectively. The relative reflectance of water is measured by using the attenuated total reflection method and a Fourier transform infrared spectrometer in both cases. The increase in relative reflectance at the wavelength range from 14.5 to 14.9 μm, corresponding to the intermolecular vibrations of water, is obtained by subtracting the relative reflectance in the conductive heating from the relative reflectance in the infrared heating. The t-test determines that the increase in relative reflectance can be considered statistically positive. It is concluded that the infrared heating that emits the radiation to the infrared absorption band of water can promote the intermolecular vibration of water better than the conductive heating with a heater. This conclusion means that the infrared heating with wavelength-selectivity in the infrared absorption band of water may enhance water evaporation more than the conductive heating.