Laser-induced decomposition and accompanying ablation dynamics of
a reactive nitrocellulose film doped
with a Cu-phthalocyanine derivative as a light absorber was
investigated by applying a nanosecond
interferometric technique. While nitrocellulose does not absorb
XeF 351 nm excimer laser pulse, the film is
heated instantaneously via rapid photothermal conversion in the doped
Cu-phthalocyanine derivative. Below
the ablation threshold, the irradiated film expanded transiently with
no permanent etching; namely, thermal
expansion and contraction processes were directly followed in the ns
time region. Above the ablation threshold
the expansion of the film was started during the excimer laser pulse,
and then explosive decomposition was
initiated, continuing in a few hundreds ns after the excitation.
Generation of shock wave and ejection of
gaseous plume were also observed by nanosecond photographic technique.
The shock wave emerged at
100−200 ns after excitation and later than the typical shock wave
formation time reported in general. The
slow formation is consistent with the slow initiation of the
decomposition, suggesting a specific ablation
process of the nitrocellulose film. Temperature elevation caused
by the excimer laser irradiation results in
an exothermic decomposition of nitrocellulose, leading to a further
temperature rise of the film. Consequently
self-acceleration of the reaction is enhanced and an explosive
self-sustaining decomposition is induced after
reaching the explosive decomposition condition. Ablation rate was
determined to be 0.63 m/s which is slower
than that of detonation but faster than that of
combustion.
The crystal structure of anhydrous diphenylcyclopropenone was determined and the structural features are compared with those in its monohydrate. The systematic variation of the molecular geometry found is attributable to the contribution from a dipolar ionic form, enhanced by the formation of the hydrogen bond.
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