Molecular dynamics simulation of infrared absorption spectra of one-dimensional ordered single-file water*

Compared with bulk water (BW), the water in nanochannels usually shows unique structural and dynamic properties, which is still unable to be effectively detected and characterized by existing experimental techniques. The spectrum is an effective technical means for studying and identifying the material composition and characteristics. In this study, the infrared absorption spectra of one-dimensional ordered single-file water (SW) confined in (6, 6) single-walled carbon nanotubes are calculated by molecular dynamics simulation. It is found that the ordered arrangement of SW results in an obvious blue shift and enhancement of the spectral peak in the 0-35 THz range relative to the bulk water. The analysis shows that this phenomenon is caused by the change of coupling weight of libration vibrations (including rock, twist and wag modes) of SW. The twist vibration mode and wag vibration mode with higher frequency are relatively easy to occur because the binding energy decreases under the single chain structure of water, which results in the blue shift and enhancement of the spectral peak. Meanwhile, the present study shows that the spectral component characteristics of SW can well predict and explain the structural and dynamic properties of SW. Further, terahertz simulation experiments show that the infrared absorption capacity of SW basically conforms with the spectral distribution characteristics.