Research Article Active Mode Remote Infrared Spectroscopy Detection of TNT and PETN on Aluminum Substrates John R. Castro-Suarez, 1,2 Leonardo C. Pacheco-Londoño, 1,3 Joaquín Aparicio-Bolaño, 4 and Samuel P. Hernández-Rivera 1 1 ALERT DHS Center of Excellence for Explosives Research, Department of Chemistry, University of Puerto Rico-Mayagüez, Mayagüez, PR 00681, USA 2 Molecular Spectroscopy Research Group, Antonio de Arevalo Technological Foundation, TECNAR, Cartagena, Colombia 3 Environmental Engineering Program, Vice-Rectory for Research, Universidad ECCI, Bogota, Colombia 4 Department of Physics, University of Puerto Rico, Ponce, PR 00732, USA Correspondence should be addressed to John R. Castro-Suarez; johncastrosuarez@gmail.com and Samuel P. Hernández-Rivera; samuel.hernandez3@upr.edu Received 17 October 2016; Revised 4 January 2017; Accepted 17 January 2017; Published 21 March 2017 Academic Editor: Christoph Krafft Copyright © 2017 John R. Castro-Suarez et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Two standoff detection systems were assembled using an infrared telescope coupled to a Fourier transform infrared spectrometer, a cryocooled mercury-cadmium telluride detector, and a telescope-coupled midinfrared excitation source. Samples of the highly energetic materials (HEMs) 2,4,6-trinitrotoluene (TNT) and pentaerythritol tetranitrate (PETN) were deposited on aluminum plates and detected at several source-target distances by carrying out remote infrared spectroscopy (RIRS) measurements on the aluminum substrates in active mode. The samples tested were placed at 1–30 m for the RIRS detection experiments. The effect of the angle of incidence/collection of the IR beams on the vibrational band intensities and the signal-to-noise ratios (S/N) were investigated. Experiments were performed at ambient temperature. Surface concentrations from 50 to 400 μg/cm 2 were studied. Partial least squares regression analysis was applied to the spectra obtained. Overall, RIRS detection in active mode was useful for quantifying the HEMs deposited on the aluminum plates with a high confidence level up to the target-collector distances of 1–25 m. 1. Introduction The detection and identification of highly energetic materials (HEMs), commonly called explosives, and related devices are an important priority for security and counterterrorism applications [1–4]. Defense and security agencies continu- ously support research and development strategies for the development of efficient sensing systems that help detect HEM. When used in public places, such as airports, stadi- ums, maritime, and railway or coach stations, these systems can help prevent or minimize damage that could be caused by terrorist attacks [4]. Investigations on the development of sensors involving analytical methodologies that enable faster, more sensitive, less expensive, and simpler determinations to facilitate the trace identification of explosives in different fields of inter- est for national defense have increased in recent years [5]. Modern detection systems are routinely used to prevent these events. These are based on ionization techniques accompanied by separation schemes, pyrolysis, gas phase reactions, interaction with radiation, color tests, immuno- chemical reactions between HEMs and their specific anti- bodies, and so forth. These techniques have proven to be useful for explosive detection in different phases (solid, liquid, and gas) on various substrates or complex matrixes (such as soil, air, and water) [5–10]. However, in most cases, they require some type of sample preparation for subsequent chemical analysis. Since each chemical substance has its own distinctive fingerprint spectrum, vibrational techniques such as Raman Hindawi Journal of Spectroscopy Volume 2017, Article ID 2730371, 11 pages https://doi.org/10.1155/2017/2730371