Spectroscopic observation of neutral carbon during photodissociation of explosive-related compounds in the vapor phase

Helena Diez-y-Riega; Hergen Eilers

doi:10.1364/AO.52.007083

Applied Optics
Vol. 52,
Issue 29,
pp. 7083-7093
(2013)
•https://doi.org/10.1364/AO.52.007083

Spectroscopic observation of neutral carbon during photodissociation of explosive-related compounds in the vapor phase

Helena Diez-y-Riega and Hergen Eilers

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Helena Diez-y-Riega and Hergen Eilers, "Spectroscopic observation of neutral carbon during photodissociation of explosive-related compounds in the vapor phase," Appl. Opt. 52, 7083-7093 (2013)

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Abstract

We perform time-resolved laser-induced fluorescence measurements of mononitrotoluenes (MNTs) and dinitrotoluenes (DNTs) in nitrogen and air. We observe the multipeak emission spectrum of NO and find that the emission peak intensity in the 247–248 nm range is stronger than expected compared to the other NO emission peak intensities. This increased emission intensity is believed to be due to neutral carbon [C(I)], which has a strong emission peak at 247.85 nm. By comparing the ratios of integrated emission peak intensities with those expected from the Franck–Condon factors for NO, we are able to identify samples that exhibit C(I) emission. We show that the DNTs exhibit C(I) emission for gate delays of 1500 ns and beyond, while the MNTs exhibit C(I) emission for gate delays of only up to about 500 ns. Carbon deposits in the analysis chamber confirm the presence of C. Ambient NO in air enhances the observed $NO + C (I)$ signal from MNTs and DNTs.

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Transition	Wavelength/nm	Franck–Condon Factor
$ν^{'} = 0 \to ν^{''} = 0$	226–227	0.16558
$ν^{'} = 0 \to ν^{''} = 1$	236–237	0.26393
$ν^{'} = 0 \to ν^{''} = 2$	247–248	0.23793
$ν^{'} = 0 \to ν^{''} = 3$	259–260	0.16062
$ν^{'} = 0 \to ν^{''} = 4$	272–273	0.090801
$ν^{'} = 0 \to ν^{''} = 5$	285–286	0.045607

Sample	Gate Delay/ns	Ratio
$NO / N_{2}$	0	$1.09 \pm 0.02$
$NO / N_{2}$	50	$1.16 \pm 0.06$
$NO / N_{2}$	500	$1.12 \pm 0.07$
$NO / N_{2}$	1500	$1.09 \pm 0.04$
NO/Air	0	$1.17 \pm 0.10$
NO/Air	50	$1.11 \pm 0.06$
NO/Air	500	$1.14 \pm 0.06$
NO/Air	1500	$1.26 \pm 0.12$

Sample	Gate Delay/ns	Ratio
$2 - NT / N_{2}$	0	$0.93 \pm 0.03$
$2 - NT / N_{2}$	50	$0.89 \pm 0.07$
$2 - NT / N_{2}$	500	$0.98 \pm 0.02$
$2 - NT / N_{2}$	1500	$1.11 \pm 0.06$
2-NT/Air	0	$0.89 \pm 0.05$
2-NT/Air	50	$0.93 \pm 0.04$
2-NT/Air	500	$0.90 \pm 0.07$
2-NT/Air	1500	$1.27 \pm 0.10$
$4 - NT / N_{2}$	0	$0.90 \pm 0.02$
$4 - NT / N_{2}$	50	$0.93 \pm 0.02$
$4 - NT / N_{2}$	500	$0.90 \pm 0.02$
$4 - NT / N_{2}$	1500	$1.05 \pm 0.04$

Sample	Gate Delay/ns	Ratio
$2, 4 - DNT / N_{2}$	0	$0.94 \pm 0.04$
$2, 4 - DNT / N_{2}$	50	$0.96 \pm 0.04$
$2, 4 - DNT / N_{2}$	500	$0.84 \pm 0.04$
$2, 4 - DNT / N_{2}$	1500	$0.90 \pm 0.08$
2,4-DNT/Air	0	$0.85 \pm 0.06$
2,4-DNT/Air	50	$0.79 \pm 0.08$
2,4-DNT/Air	500	too weak
2,4-DNT/Air	1500	too weak
$3, 4 - DNT / N_{2}$	0	$0.87 \pm 0.02$
$3, 4 - DNT / N_{2}$	50	$0.85 \pm 0.02$
$3, 4 - DNT / N_{2}$	500	$0.82 \pm 0.03$
$3, 4 - DNT / N_{2}$	1500	$0.86 \pm 0.03$
$2, 6 - DNT / N_{2}$	0	$0.90 \pm 0.02$
$2, 6 - DNT / N_{2}$	50	$0.96 \pm 0.02$
$2, 6 - DNT / N_{2}$	500	$0.90 \pm 0.03$
$2, 6 - DNT / N_{2}$	1500	$0.96 \pm 0.03$

Concentration/ppm	Ratio
1.3	0.93
1.3	0.88
0.59	0.89
0.59	0.83
0.256	0.97
0.000559	0.94
0.000559	0.93
0.000559	0.84
0.000478	0.72
0.000440	0.99
Average	$0.89 \pm 0.08$

Sample	Gate Delay/ns	Ratio
2,4-DNT/Ar	0	$0.89 \pm 0.01$
2,4-DNT/Ar	50	$0.89 \pm 0.01$
2,4-DNT/Ar	500	$0.93 \pm 0.01$
2,4-DNT/Ar	1500	$0.89 \pm 0.02$
$2, 4 - DNT / N_{2}$	0	$0.94 \pm 0.04$
$2, 4 - DNT / N_{2}$	50	$0.96 \pm 0.04$
$2, 4 - DNT / N_{2}$	500	$0.84 \pm 0.04$
$2, 4 - DNT / N_{2}$	1500	$0.90 \pm 0.08$

Sample	Gate Delay/ns	Ratio
$2 - NT (1 ppm) / NO (40 ppm) / N_{2}$	0	$0.95 \pm 0.01$
	50	$0.85 \pm 0.01$
	500	$0.96 \pm 0.02$
	1500	$1.03 \pm 0.02$
$2 - NT (1 ppm) / NO (20 ppm) / Air (10 % O_{2})$	0	$0.96 \pm 0.01$
	50	$0.97 \pm 0.02$
	500	$0.94 \pm 0.01$
	1500	$1.05 \pm 0.02$
$2, 4 - DNT (1 ppm) / NO (40 ppm) / N_{2}$	0	$0.93 \pm 0.01$
	50	$0.91 \pm 0.01$
	500	$0.90 \pm 0.01$
	1500	$0.89 \pm 0.02$
$2, 4 - DNT (1 ppm) / NO (20 ppm) / Air (10 % O_{2})$	0	$0.91 \pm 0.01$
	50	$0.93 \pm 0.01$
	500	$0.89 \pm 0.01$
	1500	$0.91 \pm 0.02$

Laser Energy/mJ/Pulse	Ratio
0.1	0.81
0.5	0.87
1.0	0.91
1.2	0.86
1.5	0.90
Average	$0.87 \pm 0.04$

Pressure/Torr	Ratio
790	0.88
573	0.93
280	0.90
92	0.83
11	0.86
Average	$0.88 \pm 0.04$

Laser Energy/mJ/Pulse	Ratio
0.1	0.81
0.5	0.87
1.0	0.91
1.2	0.86
1.5	0.90
Average	$0.87 \pm 0.04$

Pressure/Torr	Ratio
790	0.88
573	0.93
280	0.90
92	0.83
11	0.86
Average	$0.88 \pm 0.04$

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Applied Optics