一氧化碳光致脫附是低溫星際環境中重要的非熱脫附機制。過去研究多著重於純一氧化碳冰，但星際中的一氧化碳通常存在於富含水的冰幔上，其中一氧化碳與水的介面層結構可能影響其光致脫附行為。 本研究探討低溫條件下純一氧化碳冰與一氧化碳覆蓋於水冰上的層冰之光脫附行為。利用透射式紅外光譜分析懸空羥基特徵的淬滅行為，以定義一氧化碳在非晶態固態水上的表面覆蓋度。分析結果顯示，當一氧化碳厚度約為 30–36 ML 時，非晶態固態水中可接近的懸空羥基表面位點接近飽和。 真空紫外光照射實驗顯示，純一氧化碳冰與覆蓋度較高的層冰具有相似的光脫附行為，而較低的一氧化碳覆蓋度則對應較短的有效能量傳遞長度。升溫脫附實驗結果亦顯示，在較低一氧化碳覆蓋度下，與非晶態固態水相關的延遲脫附成分更為明顯。 上述結果表示，層冰樣品中的一氧化碳光脫附行為不僅受到一氧化碳總厚度影響，也與一氧化碳在非晶態固態水上的覆蓋程度及層冰介面有關。因此，在描述富含水冰幔中的一氧化碳光脫附時，應考慮介面層一氧化碳與類純一氧化碳覆蓋層對光脫附行為的不同貢獻。;CO photodesorption is an important non-thermal desorption mechanism in cold interstellar environments. While previous studies have primarily focused on pure CO ice， interstellar CO commonly resides on H2O-rich ice mantles， where the CO/H2O interfacial structure may influence photodesorption behavior. In this work， the photodesorption behavior of pure CO ice and layered CO/H2O ice was systematically investigated under low-temperature conditions. The surface coverage of CO on amorphous solid water (ASW) was determined from the quenching behavior of dangling OH (dOH) features measured by transmission infrared spectroscopy. The analysis showed that the population of accessible dOH-containing surface sites approached saturation at CO thicknesses of approximately 30–36 ML. Photodesorption experiments under vacuum ultraviolet irradiation showed that pure CO ice and thick layered CO/H2O ice exhibit similar photodesorption behavior， whereas reduced CO coverage resulted in shorter effective energy-transfer lengths. Temperature-programmed desorption (TPD) measurements further showed that the delayed desorption component associated with ASW-influenced environments became more pronounced at lower CO coverage. These results indicate that CO molecules located near or influenced by the CO/H2O interface are more strongly retained and contribute less efficiently to the photodesorption process characteristic of bulk-like CO ice. Overall， the present results suggest that CO photodesorption in H2O-rich interstellar ice mantles cannot be described solely by the total CO thickness. Instead， both the degree of CO coverage on ASW and the relative contribution of interfacial CO and bulk-like CO must be taken into account when evaluating CO photodesorption in astrochemical models.
