Collisional Relaxation of NCN: An Experimental Study with Laser-Induced Fluorescence

Abstract

Collisional relaxation of NCN produced by photolysis of NCN 3 at a wavelength of 248 nm has been investigated with laser-induced fluorescence (LIF) in a temperature range of 240-293 K and a pressure range of 10-800 mbar with different bath gases (He, Ne, Ar, Kr, H 2 , N 2 , O 2 , and N 2 O). LIF excitation spectra were recorded, and LIF intensity-time profiles experimentally obtained at an excitation wavelength of 329.01 nm have been fitted with biexponential functions. The pressure and bath gas dependence of the rate coefficients obtained was rationalized in terms of a simple Landau-Teller/Schwartz-Slawsky-Herzfeld model, and notable influences of vibrational energy transfer to the rate of the overall relaxation process have been found. Evidence was obtained for a two-channel vibrational relaxation in NCN.

Theory and modeling of relevance to prompt-NO formation at high pressure

“…A series of experimental studies by Friedrichs and coworkers who determined rate constants for several of the NCN reactions, i.e., NCN + M [21], NCN + H [22], NCN + O [21], NCN + O 2 [23], and 2 NCN + NO [24] and corresponding theoretical studies by Lin and coworkers of NCN + H [20], NCN + O [25], NCN + OH [26], and NCN + O 2 [27] have greatly expanded our understanding of the kinetics of NCN reactions. Furthermore, Olzmann and coworkers have explored the collisional relaxation [28], thermal dissociation [29], and reaction with NO [30]. Nevertheless, important aspects of both the thermochemistry and reactions of NCN are still in discussion [15,22,31] and modeling predictions of prompt NO formation have a higher degree of uncertainty than desired [16].…”

The story of NCN as a key species in prompt-NO formation

“…Additional lines around 317-320 nm corresponding to the (020) -( 000) and ( 030) -(010) bands were also observed (see Supplementary Material of Ref. [73] and Fig. 6).…”

“…The NCN band head was spectrally resolved by narrow-bandwidth (< 0.01 cm -1 ) laser absorption measurements at 293 K by Dammeier and Friedrichs [72]. Hetzler and Olzmann [73] measured a LIF excitation spectrum of NCN at 293 K with a spectral bandwidth of 1 cm -1 . The spectrum was obtained at saturated LIF conditions and is shown in Fig.…”

“…Fig. 5 presents the comparison of the experimental LIF excitation spectrum from Hetzler and Olzmann [73] with simulated spectra from the two different spectroscopic models published in 2009 [42] and 2013 [68]. For the 2013 version, many additional bands such as the (020) -(020) transitions between 325.7 and 325.9 nm were included to further improve the simulation of spectral features that are weak at room temperature but more intense at higher temperatures.…”

“…5. LIF excitation spectra of 3 NCN at 293K: experimentally obtained by saturated LIF [73] (black) and simulated (convoluted with a Gaussian linewidth of 0.6 cm -1 ) with PGOPHER by employing the parameter set used in Ref. [42] (blue) and in Ref.…”