The chemical
reactions of hot or room temperature and/or critical water in a time-range
of picosecond and sub-picoseconds have been carried out by the 18 MeV
S-band linac and a Mg photocathode RF gun with the irradiation of third
harmonic Ti: Sapphire laser, at Nuclear Engineering Research Laboratory
(NERL), the University of Tokyo. Although this short bunch and 100 fs
laser light are enough to perform the experiment of radiation chemistry
in the time-range of sub-picoseconds, the total time-resolution become
worse by the instability of synchronization between laser and radio
frequency of linac. We found that the fluctuation of room temperature
causes the instability, particularly the cycle of turning on/off of
the air-conditioner. When we decrease the fraction of the room temperature
within 0.1 degrees, the timing drift in an hour reaches 600 fs, closed
to the timing jitter of 340fs than previous results.