Laser-induced fluorescence spectroscopy of CN(X2Σ+) radicals produced by vacuum UV photoexcitation of CH3CN with synchrotron radiation

State-Resolved Dynamics of the CN(B2Σ+) and CH(A2Δ) Excited Products Resulting from the VUV Photodissociation of CH3CN

“…A further intense, broad peak is detected between 14.5−18 eV, with a maximum at 16.2 ± 0.1 eV. The lack of defined structure is in harmony with the absorption spectrum of CH 3 CN, which is a continuum at h ν > 13 eV. , This feature displays a profile over the same photon energy range nearly identical to that seen in the CN(B 2 Σ + − X 2 Σ + ) excitation spectrum recorded by Mitsuke and Mizutani . Because their detection PMT is rated to cover the 300−650 nm (15,584−33,333 cm -1 ) range, which is narrower than that of the broadband PMT used here, transitions that emit at longer or shorter emission wavelengths are unlikely to be observed in the 14.5−18 eV photon energy region displayed in Figure .…”

“…31,33 This feature displays a profile over the same photon energy range nearly identical to that seen in the CN(B 2 Σ + -X 2 Σ + ) excitation spectrum recorded by Mitsuke and Mizutani. 34 Because their detection PMT is rated to cover the 300-650 nm (15,584-33,333 cm -1 ) range, which is narrower than that of the broadband PMT used here, transitions that emit at longer or shorter emission wavelengths are unlikely to be observed in the 14.5-18 eV photon energy region displayed in Figure 1. Therefore, when the relevant thermochemistry is also considered (Tables 1 and 2), it is highly probable that the broad feature comprises emission from the CN(B 2 Σ + ), CH(A 2 ∆), CH(B 2 Σ -), and CH(C 2 Σ + ) excited states to their respective ground states.…”

“…65 However, thermodynamics indicate that there is insufficient energy to form either excited CN* or CH* fragments with ionic partners: 45,66 Furthermore, a comparison of the cross section for production of CH 3 + from CH 3 CN by a 15.6 eV photon (0.1 × 10 -18 cm 2 ) with the total absorption cross section for CH 3 CN at the same energy (43 × 10 -18 cm 2 ) gives a branching ratio for CH 3 + formation of only ≈0.2%. 33,34 Because the fluorescence quantum yields for CN(B 2 Σ + -X 2 Σ + ) and CH* (from CH 4 ) at 16 eV are 10% and ≈5%, respectively, 33,67 it is implausible that either CN(B 2 Σ + -X 2 Σ + ) or CH(A 2 ∆-X 2 Π) emission is occurring in conjunction with ionization in a single photon event. Once again, the T rot data derived from the 16 eV spectrum can be compared to reactions in a flowing afterglow performed elsewhere, 39 although this time the reactive argon species is Ar + .…”

“…14,32,33 Mitsuke and Mizutani utilized a novel synchrotron pump-LIF probe scheme to study the ground state CN(X 2 Σ + ) radicals produced when CH 3 CN interacts with 13.6-18.6 eV photons. 34 Cody et al used an argon lamp pump-LIF probe experiment to examine the CN(X 2 Σ + ) fragments produced at hν < 9.5 eV under high collision frequency conditions (P ) 133 Pa). 35 Ashfold and Simons 36 and Moriyama et al 37 have performed some work that is most pertinent to this study; comparisons to the findings of these two studies will be performed in this article.…”

“…Previous fundamental research on the CH 3 CN molecule in the VUV region includes several photoabsorption studies using noble gas resonance lamps and synchrotron light sources. ,, Mitsuke and Mizutani utilized a novel synchrotron pump−LIF probe scheme to study the ground state CN(X 2 Σ + ) radicals produced when CH 3 CN interacts with 13.6−18.6 eV photons …”