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[MIS26-P02] Crystallographic characteristics of nitric oxide hydrate
Keywords:gas hydrate, hydration number, nitric oxide
Nitric oxide is one of the interstellar materials, and gas hydrates containing nitric oxide are interesting materials in the field of space and planetary science. However, due to the high reactivity of nitric oxide, there has been only one report (Hallbrucker, 1994) of the formation of nitric oxide hydrate where the hydrate was formed by contacting amorphous ice with nitric oxide. In this study, we attempted to form samples by contacting fine hexagonal ice powder with nitric oxide gas. We also measured the equilibrium pressure of nitric oxide hydrate, which has been unknown until now. Powder X-ray diffraction measurement, Raman spectroscopic analysis, calorimetry, and hydration number estimation were also carried out on the sample of nitric oxide hydrate.
Fine ice powder was produced by scraping ice frozen from distilled water using a microtome, and was sealed in a pressure cell with nitric oxide gas. The temperature of the cell was controlled from 77 K to 273 K, and the hydrate sample was formed by contacting the melt water with the gas. The sample was then fixed at 77 K while degassing with a vacuum pump. Powder X-ray diffraction was used for determination of crystallographic structure. Raman spectroscopic analysis was performed on this sample and Raman peaks attributed to molecular vibration of enclathrated nitric oxide were observed. Calorimetric measurement was carried out to determine the dissociation heat of the hydrate samples. The equilibrium pressure of hydrate was measured by creating a coexistence of hydrate, water, and gas in a pressure cell and controlling the temperature using a thermostatic bath at around 273 K.
The crystallographic structure of the hydrate sample was determined as the cubic structure II. Hallbrucker (1994) reported that the N-O stretching vibration of the sample containing nitric oxide hydrate appeared at 1836.6 cm-1, 1858.8 cm-1, and 1867.8 cm-1. In this experiment, they corresponded to the peaks observed at 1838 cm-1, 1862 cm-1 and 1871 cm-1, respectively. The thermograph obtained from the calorimetry was analyzed and the dissociation heat from hydrate to gas and ice was calculated to be 15.7 kJ mol-1, assuming that the negative peaks of heat flow with increasing the pressure correspond to the dissociation heat of hydrate. From the dataset of the equilibrium pressure at around 273 K, the dissociation heat from hydrate to gas and water was calculated to be 59.5 kJ mol-1 using the Claudius-Clapeyron equation. From these values of dissociation heat, the hydration number of nitric oxide hydrate was estimated to be 7.3.
Reference
Hallbrucker A (1994) A clathrate hydrate of nitric oxide. Angew Chem Int Ed Engl 33: 691-693
Fine ice powder was produced by scraping ice frozen from distilled water using a microtome, and was sealed in a pressure cell with nitric oxide gas. The temperature of the cell was controlled from 77 K to 273 K, and the hydrate sample was formed by contacting the melt water with the gas. The sample was then fixed at 77 K while degassing with a vacuum pump. Powder X-ray diffraction was used for determination of crystallographic structure. Raman spectroscopic analysis was performed on this sample and Raman peaks attributed to molecular vibration of enclathrated nitric oxide were observed. Calorimetric measurement was carried out to determine the dissociation heat of the hydrate samples. The equilibrium pressure of hydrate was measured by creating a coexistence of hydrate, water, and gas in a pressure cell and controlling the temperature using a thermostatic bath at around 273 K.
The crystallographic structure of the hydrate sample was determined as the cubic structure II. Hallbrucker (1994) reported that the N-O stretching vibration of the sample containing nitric oxide hydrate appeared at 1836.6 cm-1, 1858.8 cm-1, and 1867.8 cm-1. In this experiment, they corresponded to the peaks observed at 1838 cm-1, 1862 cm-1 and 1871 cm-1, respectively. The thermograph obtained from the calorimetry was analyzed and the dissociation heat from hydrate to gas and ice was calculated to be 15.7 kJ mol-1, assuming that the negative peaks of heat flow with increasing the pressure correspond to the dissociation heat of hydrate. From the dataset of the equilibrium pressure at around 273 K, the dissociation heat from hydrate to gas and water was calculated to be 59.5 kJ mol-1 using the Claudius-Clapeyron equation. From these values of dissociation heat, the hydration number of nitric oxide hydrate was estimated to be 7.3.
Reference
Hallbrucker A (1994) A clathrate hydrate of nitric oxide. Angew Chem Int Ed Engl 33: 691-693