研究目的
Calculating the volumetric thermal expansion coefficient of a-nitrogen (N2) ice for temperatures between 10 and 25 K using terahertz transmission data and a phonon model.
研究成果
A phonon model and experimental terahertz transmission data of a-N2 ice were utilized to calculate the lattice parameters of a-nitrogen ice between 10 and 25 K. The thermal expansion coefficient values are in good agreement with reported literature values within 0.3% deviation in the Lennard-Jones length parameter.
研究不足
The study assumes that the Lennard-Jones parameters and quadrupole moment of a pair of N2 molecules do not change between 10 and 25 K. The deviation in thermal expansion coefficient values from those measured using dilatometry and XRD could be due to different sample preparation methods and the presence of impurities or defects.
1：Experimental Design and Method Selection:
The study uses terahertz time-domain spectroscopy to measure the transmission coefficient of a-N2 ice at various temperatures. A phonon model based on an intermolecular potential combining Lennard-Jones and quadrupole–quadrupole interaction terms is employed to analyze the data.
2：Sample Selection and Data Sources:
a-N2 ice samples were grown on a sapphire substrate at 10 K and vacuum pressure of 6 l torr in a cryostat by vapor deposition.
3：List of Experimental Equipment and Materials:
A 45 GHz spectral resolution terahertz time-domain spectrometer was used for data acquisition.
4：Experimental Procedures and Operational Workflow:
The transmission data were acquired for temperatures between 10 and 25 K. The central frequency of the absorption feature around 1.45 THz was monitored as a function of temperature.
5：45 THz was monitored as a function of temperature.
Data Analysis Methods:
5. Data Analysis Methods: The lattice parameters of a-N2 ice were obtained by minimizing the deviation-square of the experimental resonant frequencies and the model-based frequencies.
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