The infrared absorption spectrum of carbon dioxide ice from 1.8 to 333 μm
The infrared absorption spectrum of carbon dioxide ice from 1.8 to 333 μm
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二氧化碳冰1.8~333μm的红外吸收光谱
DOI：
10.1029/97je01875
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发表时间：
1997
影响因子：
--
通讯作者：
G. Hansen
中科院分区：
文献类型：
--
作者：
G. Hansen
例如，需要固体二氧化碳的光学常数来精确计算火星季节性极冠的能量平衡，这些极冠主要由二氧化碳冰组成。在固体CO2孤立的窄红外吸收带之间的宽波长弱吸收区域，只有少数测量的准确性不确定，这决定了这些极冠的反射率和发射率。因此，进行了一项实验室实验，通过测量高质量厚样品的透射率来改进和扩展先前数据的波长范围，以确定1.8至333 μm（波数为30-5555 cm−1）之间低吸收红外波长区域的光谱吸收系数α。开发了一种技术，在150 K的温度下从气体中生长出清晰、厚的CO2冰样品，光程长度在1.6和107.5 mm之间。所有厚度的透射率数据被组合在一个最小化程序中，该程序估计每个样品的散射损耗（通常<20%消光）和每个波长的α（在0.1至4000 m−1之间），假设散射随波长缓慢变化。还估计了导出的吸收系数的准确性，并且在α不接近测量极限的区域中是最好的。从新的测量中获得的吸收系数比先前在强红外波段之间的透明波长区域的估计低一个数量级或更多。此外，许多在1.8和5.2 μm之间的弱带，以前定义不好，已经被更精确地测量。
The optical constants of solid carbon dioxide are needed, for example, to accurately calculate the energy balance of the seasonal polar caps of Mars, which are composed primarily of CO2 ice. Only a few measurements of uncertain accuracy have been made in the broad wavelength regions of weak absorption between the isolated narrow infrared absorption bands of solid CO2, which determine the reflectance and emissivity of these polar caps. A laboratory experiment was therefore undertaken to improve on and extend the wavelength range of the previous data by measuring transmission through thick samples of high quality to determine the spectral absorption coefficient α in infrared wavelength regions of low absorption between 1.8 and 333 μm (30–5555 cm−1 in wavenumber). A technique was developed to grow clear, thick CO2 ice samples from the gas at a temperature of 150 K, with optical path lengths between 1.6 and 107.5 mm. The extremely fine spectral structure of this material was measured using resolutions finer than 0.5 cm−1. The transmission data for all thicknesses are combined in a minimizing routine that estimates both the scattering losses for each sample (typically <20% extinction) and α (between ∼0.1 to 4000 m−1) at each wavelength, on the assumption that the scattering varies slowly with wavelength. The accuracy of the derived absorption coefficients was also estimated and is best in regions where α is not near the limits of measurement. Absorption coefficients obtained from the new measurements are an order of magnitude or more lower than earlier estimates in the transparent wavelength regions between the strong infrared bands. Also, many weak bands between 1.8 and 5.2 μm, which were only poorly defined previously, have been more accurately measured.