Time-Of-Flight Mass Spectrometry of Laser Exploding Foil Initiated PETN Samples

We report the results of time-of-flight mass spectrometry (TOFMS) measurements of the gaseous products of thin film PETN samples reacting \textit{in-vacuo}. The PETN sample spots are produced by masked physical vapor deposition of PETN [A.S. Tappan, \textit{et al}., AIP Conf. Proc. \textbf{1426}, 677 (2012)] onto a first-surface aluminum mirror. A pulsed laser beam imaged through the soda lime glass mirror substrate converts the aluminum layer into a high-temperature high-pressure plasma which initiates chemical reactions in the overlying PETN sample. We had previously proposed [E.C. Fossum, \textit{et al}., AIP Conf. Proc. \textbf{1426}, 235 (2012)] to exploit differences in gaseous product chemical identities and molecular velocities to provide a chemically-based diagnostic for distinguishing between ``detonation-like'' and deflagration responses. Briefly: we expect in-vacuum detonations to produce hyperthermal (v $\sim$ 10 km/s) thermodynamically-stable products such as N$_{2}$, CO$_{2}$, and H$_{2}$O, and for deflagrations to produce mostly reaction intermediates, such as NO and NO$_{2}$, with much slower molecular velocities -- consistent with the expansion-quenched thermal decomposition of PETN. We observe primarily slow reaction intermediates (NO$_{2}$, CH$_{2}$NO$_{3})$ at low laser pulse energies, the appearance of NO at intermediate laser pulse energies, and the appearance of hyperthemal CO/N$_{2}$ at mass 28 amu at the highest laser pulse energies. However, these results are somewhat ambiguous, as the NO, NO$_{2}$, and CH$_{2}$NO$_{3}$ intermediates persist and all species become hyperthermal at the higher laser pulse energies. Also, the purported CO/N$_{2}$ signal at 28 amu may be contaminated by silicon ablated from the glass mirror substrate. We plan to mitigate these problems in future experiments by adopting the ``Buelow'' sample configuration which employs an intermediate foil barrier to shield the energetic material from the laser and the laser driven plasma [S.J. Buelow, \textit{et al}., AIP Conf. Proc. \textbf{706}, 1377 (2003)]. [RW PA{\#}4930]