Laser‐Induced‐FluorescenceSpectrum of the CNN Molecule

Abstract

We have recorded a laser excitation spectrum of the A3Π–X3Σ− electronic band system of the CNN radical in the gas phase, at a resolution of ca. 0.8 cm−1. The rotational branch structure of the vibrational band near 419 nm has been simulated and molecular parameters are obtained. The results are compared with data from laser-induced-fluorescence spectra of CNN trapped in a low-temperature matrix. A revised value for the spin-orbit parameter in the A3Π state is obtained and comparison is made with the values for related molecules. The possible detection of CNN in astrophysical sources is considered and the general features of its rotational spectrum in the ground electronic state are described.

Photodissociation dynamics of the CNN free radical

“…The laser fluences were typically 200 mJ/cm 2 for photon energies between 23 500-24 200 ͑i.e., peaks A-C͒ and 80 mJ/cm 2 from 24 700-26 000 cm Ϫ1 ͑remainder of spectrum͒. A broad feature with a width of Ϸ 100 cm Ϫ1 is observed near 23 850 cm Ϫ1 ͑A͒ in good agreement with the rotationally resolved origin band observed by Curtis et al 14 Weaker features, B and C, observed 200 and 300 cm Ϫ1 to the blue of the origin are most likely due to sequence bands involving vibrationally excited levels of the ground state. As discussed below, peak A results from twophoton dissociation, which is why such high laser fluence was needed.…”

“…Feature F displays three prominent subbands with a spacing of Ϸ27 cm Ϫ1 and a broader peak between the first two of these. The subband spacing of 27 cm Ϫ1 is close to the spin-orbit splitting, A ϭϪ26.5 cm Ϫ1 reported for the 000-000 band observed at lower energy in the experiments of Curtis et al 14 The most intense subband possesses a width of about 1.5 cm Ϫ1 . Feature E, in contrast, does not possess any obvious subband structure; it consists of a peak at 25 044 cm Ϫ1 that is 3 cm Ϫ1 wide and a smaller feature Ϸ11 cm Ϫ1 to the red.…”

“…With the aid of previous gas-phase 14 and matrix 6,11 LIF studies, we have been able to assign several vibronic features of the à 3 ⌸←X 3 ⌺ Ϫ . PFY spectra are a convolution of both absorption and dissociation and may therefore exhibit different structure than emission or absorption-based techniques.…”

“…Gas-phase optical spectroscopic data for CNN is limited to low resolution UV absorption studies by Braun et al, 13 who observed transitions at 23 870 and 25 190 cm Ϫ1 , and a rotationally resolved LIF spectrum of the à 3 ⌸←X 3 ⌺ Ϫ origin by Curtis et al, 14 yielding a gas-phase spin-orbit splitting, AϭϪ26.5 cm Ϫ1 . These authors also reported a sequence band Ϸ 145 cm Ϫ1 above the origin.…”

Photodissociation dynamics of the singlet and triplet states of the NCN radical

“…This is consistent with the experimental observation of both isomers as distinct species. [25][26][27][28][29][30] The NCN radical provides as rich system for photodissociation studies. It has several low-lying singlet and triplet excited states above the dissociation limit as well as multiple energetically accessible product states, as shown in Fig.…”