Presentation Information
[MIS19-04]Experimental Study on the Formation of H2O Ice Nanoparticles in the Gas Phase
*Kanji Sakai1, Yuki Kimura1, Tomoya Yamazaki1 (1.Hokkaido University)
Keywords:
Nucleation
Water in space is formed on dust grain surfaces as ice in molecular clouds, and it plays an important role in material evolution in star forming regions and protoplanetary disks. These ices can be sublimated during the formation of stars and planetary systems and then recondense as the gas cools1. During this recondensation process, the size and number density of ice particles change, which may influence molecular evolution and the composition of planetary materials. Recondensation proceeds under nonequilibrium conditions and therefore involves nucleation. In the Earth’s atmosphere, condensation of water and ice formation have been extensively studied, and they are understood to occur predominantly via heterogeneous nucleation². In contrast, in astrophysical environments, the nucleation and early growth processes of ice particles formed from water vapor via homogeneous nucleation under low density conditions remain insufficiently understood3.
In this study, we attempted to experimentally reproduce the recondensation process of ice in astrophysical environments. Ice nanoparticles formed from the gas phase were investigated by in-situ IR spectroscopy, and the generated particles were collected and observed by transmission electron microscopy (TEM) to examine the formation process from nucleation to early growth.
The experiment was performed using a low temperature nucleation chamber developed in our laboratory. The chamber has a double tube structure cooled with liquid nitrogen between the walls. After evacuating the chamber, nitrogen gas was introduced and water vapor was generated by heating an evaporation source. The water vapor was cooled through collisions with the surrounding gas, leading to the formation of ice nanoparticles via homogeneous nucleation. This process was monitored by in-situ IR spectroscopy. The particles were directly collected on TEM grids using a cryo transfer holder installed inside the chamber and observed by TEM while maintaining low temperature.
TEM observations revealed particles ranging from several tens of nanometers to several micrometers in size. Electron diffraction patterns indicated that most of the generated particles were amorphous ice.
[1] J. I. Lunine et al., Icarus, 1991, 94, 333–344.
[2] C. Hoose et al., ACP, 2012, 12, 9817-9854.
[3] A. C. A. Boogert et al., Annu. Rev. Astron. Astrophys., 2015, 53, 541–581.
In this study, we attempted to experimentally reproduce the recondensation process of ice in astrophysical environments. Ice nanoparticles formed from the gas phase were investigated by in-situ IR spectroscopy, and the generated particles were collected and observed by transmission electron microscopy (TEM) to examine the formation process from nucleation to early growth.
The experiment was performed using a low temperature nucleation chamber developed in our laboratory. The chamber has a double tube structure cooled with liquid nitrogen between the walls. After evacuating the chamber, nitrogen gas was introduced and water vapor was generated by heating an evaporation source. The water vapor was cooled through collisions with the surrounding gas, leading to the formation of ice nanoparticles via homogeneous nucleation. This process was monitored by in-situ IR spectroscopy. The particles were directly collected on TEM grids using a cryo transfer holder installed inside the chamber and observed by TEM while maintaining low temperature.
TEM observations revealed particles ranging from several tens of nanometers to several micrometers in size. Electron diffraction patterns indicated that most of the generated particles were amorphous ice.
[1] J. I. Lunine et al., Icarus, 1991, 94, 333–344.
[2] C. Hoose et al., ACP, 2012, 12, 9817-9854.
[3] A. C. A. Boogert et al., Annu. Rev. Astron. Astrophys., 2015, 53, 541–581.