N. Kawanaka

Photodissociation of polycrystalline and amorphous water ice films at 157 and 193 nm

The photodissociation dynamics of amorphous solid water (ASW) films and polycrystalline ice (PCI) films at a substrate temperature of 100 K have been investigated by analyzing the time-of-flight (TOF) mass spectra of photofragment hydrogen atoms at 157 and 193 nm. For PCI films, the TOF spectrum recorded at 157 nm could be characterized by a combination of three different (fast, medium, and slow) Maxwell-Boltzmann energy distributions, while that measured at 193 nm can be fitted in terms of solely a fast component. For ASW films, the TOF spectra measured at 157 and 193 nm were both dominated by the slow component, indicating that the photofragment H atoms are accommodated to the substrate temperature by collisions. H atom formation at 193 nm is attributed to the photodissociation of water species on the ice surface, while at 157 nm it is ascribable to a mixture of surface and bulk photodissociations. Atmospheric implications in the high latitude mesopause region of the Earth are discussed.

Measurements of Energy Partitioning in H2 Formation by Photolysis of Amorphous Water Ice

We demonstrate experimentally that photodissociation of amorphous solid water at 100 K results in formation of H2 molecules with an ortho/para ratio of gOPR = 3. Two distinct mechanisms can be identified: endothermic abstraction of a hydrogen atom from H2O by a photolytically produced H atom yields vibrationally cold H2 products, whereas exothermic recombination of two H-atom photoproducts yields translationally and internally hot H2. These results are in accord with predictions by molecular dynamics calculations and their astrophysical implications are discussed.

Release of hydrogen molecules from the photodissociation of amorphous solid water and polycrystalline ice at 157 and 193 nm.

The production of H(2) in highly excited vibrational and rotational states (v=0-5, J=0-17) from the 157 nm photodissociation of amorphous solid water ice films at 100 K was observed directly using resonance-enhanced multiphoton ionization. Weaker signals from H(2)(v=2,3 and 4) were obtained from 157 nm photolysis of polycrystalline ice, but H(2)(v=0 and 1) populations in this case were below the detection limit. The H(2) products show two distinct formation mechanisms. Endothermic abstraction of a hydrogen atom from H(2)O by a photolytically produced H atom yields vibrationally cold H(2) products, whereas exothermic recombination of two H-atom photoproducts yields H(2) molecules with a highly excited vibrational distribution and non-Boltzmann rotational population distributions as has been predicted previously by both quantum-mechanical and molecular dynamics calculations.

Vacuum ultraviolet photodissociation and surface morphology change of water ice films dosed with hydrogen chloride

Time-of-flight (TOF) spectra of photofragment H atoms from the photodissociation of water ice films at 193 nm were measured for amorphous and polycrystalline water ice films with and without dosing of hydrogen chloride at 100-145 K. The TOF spectrum is sensitive to the surface morphology of the water ice film because the origin of the H atom is the photodissociation of dimerlike water molecules attached to the ice film surfaces. Adsorption of HCl on a polycrystalline ice film was found to induce formation of disorder regions on the ice film surface at 100-140 K, while the microstructure of the ice surface stayed of polycrystalline at 145 K with adsorption of HCl. The TOF spectra of photofragment Cl atoms from the 157 nm photodissociation of neutral HCl adsorbed on water ice films at 100-140 K were measured. These results suggest partial dissolution of HCl on the ice film surface at 100-140 K.

Search for GeV Gamma-ray Counterparts of Gravitational Wave Events by CALET

We present results on searches for gamma-ray counterparts of the LIGO/Virgo gravitational-wave events using CALorimetric Electron Telescope ({\sl CALET}) observations. The main instrument of {\sl CALET}, CALorimeter (CAL), observes gamma-rays from

Energy Spectrum of Cosmic-Ray Electron and Positron from 10 GeV to 3 TeV Observed with the Calorimetric Electron Telescope on the International Space Station

\sim1

Release of oxygen atoms and nitric oxide molecules from the ultraviolet photodissociation of nitrate adsorbed on water ice films at 100 K

GeV up to 10 TeV with a field of view of nearly 2 sr. In addition, the {\sl CALET} gamma-ray burst monitor (CGBM) views

On-orbit operations and offline data processing of CALET onboard the ISS

\sim

Photodissociation dynamics of OCS and CS2 adsorbed on water ice films at 193 nm

3 sr and

Extended Measurement of the Cosmic-Ray Electron and Positron Spectrum from 11 GeV to 4.8 TeV with the Calorimetric Electron Telescope on the International Space Station

\sim2\pi