Mid-Infrared Imaging Spectroscopy of N2O Solid Simulating the haze of trans-Neptunian objects

\ Nitrous oxide (N$_2$O) ice is likely to exist in trans-Neptunian objects such as Pluto and Triton, potentially formed through ultraviolet (UV) radiation from the Sun or cosmic ray irradiation of N$_2$ and CO ices. However, the mid-infrared spectral characteristics of N$_2$O ice in higher temperature regions (90-110 K), changes in mid-infrared spectra during UV irradiation, and the chemical network of nitrogen oxide (N$_x$O$_y$) ices remain insufficiently understood. This study aims to elucidate these aspects through in-situ mid-infrared spectral measurements of cryogenic particles using two-dimensional imaging Fourier transform infrared spectroscopy. Spectroscopic imaging confirmed strong absorption at 7.75 $\mu$m (N$_2$O $\nu_1$ vibrational mode), with weaker vibrational modes observed at 8.60 $\mu$m (N$_2$O 2$\nu_2$), 7.27 $\mu$m (N$_2$O torsion), and 5.29 $\mu$m (N$_2$O $\nu_1$+$\nu_2$). Annealing experiments simulating high-temperature conditions demonstrated that all vibrational modes irreversibly intensified with increasing temperature, indicating progressive crystallization. New spectral features appeared at approximately 12 $\mu$m and 14 $\mu$m at the condensed sample. N$_2$O ice was exposed to ultraviolet radiation (190-340 nm) using a D$_2$ lamp for 8.5 hours to investigate spectral changes during UV irradiation. After 60-90 minutes of irradiation, all N$_2$O vibrational modes disappeared, while absorption intensities of various nitrogen oxides, including NO, NO$_2$, N$_2$O$_3$, and O$_3$ increased. Beyond 180 minutes, vibrational modes of multiple nitrogen oxide ices exhibited intensity variations across different wavelengths, corresponding to other species such as cis-(NO)$_2$, N$_2$O$_4$, and N$_2$O$_5$.