Thermal decomposition of NCN(3) as a high-temperature NCN radical source: singlet-triplet relaxation and absorption cross section of NCN((3)Σ).
The potential of the thermal decomposition of cyanogen azide (NCN3) as a high-temperature cyanonitrene (NCN) source has been investigated in shock tube experiments. Electronic ground-state NCN(3Σ) radicals have been detected by narrow-bandwidth laser absorption at overlapping transitions belonging to the Q1 branch of the vibronic 3Σ+−3Π subband of the vibrationally hot 3Πu(010)−3Σg−(010) system at = 30383.11 cm(-1) (329.1302 nm). High-temperature absorption cross sections σ have been directly measured at total pressures of 0.2−2.5 bar, log[σ/(cm2 mol(-1))] = 8.9−8.3 × 10(-4) × T/K (±25%, 750 < T < 2250 K). At these high temperatures, NCN(3Σ) formation is limited by a slow electronic relaxation of the initially formed excited NCN(1Δ) radical rather than thermal decomposition of NCN3. Measured temperature-dependent collision-induced intersystem crossing (CIISC) rate constants are best represented by kCIISC/(cm3 mol(-1) s(-1)) = (1.3 ± 0.5) × 1011 exp[−(21 ± 4) kJ/mol/RT] (740 < T < 1260 K). Nevertheless, stable NCN concentration plateaus have been observed, showing that NCN3 is an ideal precursor for NCN kinetic experiments behind shock waves.
Institut für Physikalische Chemie, Olshausenstrasse 40, Christian-Albrechts-Universität zu Kiel, D-24098 Kiel, Germany.
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J
Dammeier
G
G
Friedrichs