Comparison of polyimide film surface properties exposed to real and simulated space environments: Relevance of atomic oxygen effects to wettability in space - Polyimides and Other High Temperature Polymers - page 420

the acceleration of atomic oxygen was provided by the multiphoton absorption
process. The atomic oxygen beam, thus generated, was characterized by the time-
of-flight (TOF) distribution measured by the quadrupole mass spectrometer in-
stalled in the beam line. Translational energies of the species in the beam were
calculated using TOF distributions with a flight length of 181 cm. Every mass to
charge ratio (m/z) from 1 to 200 was scanned. However, only m/z 16 and 32,
which correspond to atomic oxygen and molecular oxygen, respectively, were de-
tected. Figure 2 represents typical translational energy distributions of m/z = 16
and 32. We used the transitional energy distribution relation P(E) ∝ t 2 N(t) to cal-

culate the translational energy, where P(E) is the number of atoms with transla-
tional energy E, and N(t) the number of atoms arrived at time t (t: the flight time).
The mean energy of the hyperthermal atomic oxygen beam was calculated to be
4.7 eV, whereas that of molecular oxygen, which is included in the beam, was 5.0
eV. The atomic oxygen fraction in the beam was approximately 45%, the balance
being molecular oxygen (thermal and hyperthermal). The atomic oxygen flux of
the beam was measured by a silver-coated quartz crystal microbalance (QCM)
with an accommodation coefficient of 1.0. A typical atomic oxygen flux at the
sample position, 134 cm away from the nozzle throat, was calculated to be 2.6 x
10 13 atoms/cm 2 /s.

Figure 1. Schematic of the laser detonation atomic oxygen beam facility used in this study.