CN radical

The HCN concentration is probably reduced mainly by the oxidation of the CN radicals [14,15],... 

The initiator gives the carbon radical (CH3)2C(CN),(Radical) which abstracts an H from the tin compound. 

The reaction of CBr4 with potassium is reported to generate free C atoms and the rate constants for reaction with methane, ethylene, and benzene have been reported. The reaction of nitrogen atoms with CN radicals has also been used as a C atom source. Carbon atoms have also been produced by passing organics through a microwave discharge. ... 

Vinyiidene Resins (Poly vinyiidene Resins), These are resins in which the unit structure in the polymer molecule is (-H2C.CX2—). Here the X usually stands for F, Cl or CN radical. Examples are Saran , Viton A and "Gene-1132A ... 

Basco and Norrish25 flash photolyzed C2N2 and BrCN in the presence of NO and observed vibrationally excited nitric oxide. They suggested that it was formed through near-resonance vibration-vibration energy exchange with CN radicals and/or in the photolysis of NCNO. 

Basco and Norrish25 followed the rate of decay of CN radicals produced in the flash photolysis of either C2N2 or BrCN. With NO present, the decay was enhanced. From an analysis of the data, a rate constant for the NO—CN reaction was deduced. It is either 2 x 109 M 1 sec-1 or 1 x 1011 M 2 sec-1 with N2 as a chaperone, depending... 

Donovan and Konstantatos (315) have made flash photolysis studies of ICN in the region above 2000 A. They have found that I(2P,/2) atoms are less than 5% of the total I atoms produced and have concluded CN radicals carry over 80% of the excess energy (about 2 eV) as translational energy. Ling and Wilson (638) have measured translational energies of the fragments, CN and I, produced from the laser photolysis of ICN at 2662 A. 

Contrary to a conclusion (315) that CN carries most of the excess energy as translational energy, Ling and Wilson (638) have found that CN radicals are produced in two different internally excited states, one probably in the <42n state (60%) and the other in the vibrationally and rotationally excited... 

Linglcman (336) has found vibrationally excited CN radicals in the Hash photolysis of BrCN in the near ultraviolet. The vibrational excitation is considered to arise from the following reaction sequence... 

Photodissociation dynamics studies in a nozzle-cooled beam have been reported along with an elegant analysis of the data (146). Only CN radicals in the v" = 0 level are reported because of the difficulty of detecting small amounts of excited radicals in the upper vibrational level. The results that were obtained by fitting the observed rotational distributions with Boltzmann rotational distribution functions are summarized in Table 3. 

Recently Shokoohi et al. (14) obtained high resolution LIF spectra from the photolysis of ICN at 266 nm. Using these spectra, they were able to show that the population of the and F2 spin components associated with each rotational level varied with both rotational and vibrational quantum number. For CN radicals with v" = 0 and N" < 43 the population of F- level < F level, for N" = 43 the population of F- level F level, and for N" > 43 the population of F- level > F2 level. In the v" = 1 level more of the CN radicals are produced in the upper N" levels than in the lower levels and for these upper levels the population of F-l level > F2 level. In the v" = 2 level, no radicals are observed below N" = 17, and the population of Fj level > F level. These results can be qualitatively understood in the following manner. The iodine atom can be produced in the /2 and the spin-orbit states. Spin-orbit interaction between... 

Recently Long and Reilly (150) have investigated the photodissociation dynamics of ICN at 157.8 nm using a F laser to dissociate the molecule. The quantum state distribution of the CN radicals produced in the B state was measured by dispersing the direct fluorescence from this state using a 3/4 nm monochromator in the second order. Their results indicate that the B state is... 

There is a recent indication that a few CN radicals may be produced in the (A II) state (156). An LIF spectra obtained in a static gas cell in the photolysis of BrCN at 193 nm by these authors is given in Figure 8. The spectra were obtained after several collisions with BrCN and show that both v" = 0 and v" = 1 levels are present in the system. This spectrum is comparable to an earlier LIF spectrum of the LeBlanc system of CN (157). 

They only observed an LIF spectra at 266 nm. The experiments were done in a static gas cell as well as in a pulsed molecular beam. In the static gas cell experiments, the CN radicals are formed in the v" = 0, 1, and 2 levels. The highest rotational level observed for the v" = 0 and v" = 1 levels of the X state... 

Other than the earlier work reviewed by Ashfold et al. (3), only three studies on the photodissociation dynamics have been reported for this molecule (153,154,158). The first study reported the quantum state distribution of the CN radical obtained in an effusive molecular beam and in a static gas cell, while the second study reported the observations in a pulsed molecular beam. The dynamics remains the same despite the fact that the initial internal state distribution of the C1CN molecule changes. This of course shows that hot bands are not important in the photodissociation of this molecule at this wavelength. 

Recently Li et al. (156) have observed that a small amount of CN radicals are formed in the A II state in the 193 nm photolysis of C1CN. An example of the LIF spectra that they obtained is shown in Figure 9. At the pressure and delay time of this spectrum the radical would have undergone some collisions so that little can be said about the nascent rotational distribution. 

This molecule is ideal for photodissociation dynamics studies, since it has allowed excited states in the visible region of the spectrum which is more easily accessible with tunable lasers. Both products can in principle be detected using the LIF method, though at the present time only the product distribution of the CN radical has been measured, since NO is often present as an impurity. The spectroscopy is also well studied... 

The latter process is not competitive with the former above the thermodynamic threshold. Furthermore, as long as the available energy was kept below the thermochemical threshold for the production of vibrationally excited CN radicals, it was possible to fit the observed rotational distributions with phase space theory. The upper electronic state that is involved in the two-photon dissociation was shown to originate below 22,000 cm l and is thought to be repulsive. It could be the same state that has its absorption maximum at 270 nm. 

The same authors were able to measure the high-resolution absorption spectrum of NCNO by detecting the two-photon photodissociation product rotationally hot CN radicals as a function of wavelength. This method allowed them to assign the constants for the ground and excited states. 

The electronic states of the CN radical have been fully characterized by Schaefer and Heil (90). Ground state CN(X2E+) has a triple bond between the carbon and nitrogen atoms, and an unpaired electron localized on the carbon atom. Collinear approach of two CN(X E+) singlet-coupled radicals leads to the... 

Figure 3 Contour plot of the difference Ap° between the electron density of NCCN and the densities of the CN radicals (contour values 0.001, +0.002, +0.005, +0.01, +0.02, +0.05, +0.1, +0.2, +0.5, 0.0 e bohr 3). Asterisks indicate the positions of the nuclei.

In the next section, we will discuss in some detail the example of bonding between two CN radicals, where the bond between the singly occupied 5a orbitals is heavily influenced by the presence of the fully occupied 4a N lone pair orbital. In this case there is, in contrast to the case of Li2, not only overlap between the singly occupied unpaired electron orbital (2s and 5a, respectively) and the opposite closed shell (Is and 4a, respectively), there is also considerable overlap between the 4a orbitals, contributing strongly to the Pauli repulsion. This Pauli repulsion, as well as the Pauli repulsion with the 5a electrons, will of course be different for the different bonding modes (NC—CN, CN—CN, and CN—NC). A detailed analysis is provided in the next section. 

As an example, we take the electron pair bonds of NC—CN and CN— NC in ct symmetry between the 5a singly occupied highest occupied orbitals (SOMOs) of the two CN radicals, two systems treated in the next section. Below the 5ct orbitals, there are fully occupied orbitals, the most important one being the 4a N lone pair orbital (the aHOMo orbital, see next section). The wavefunction VF° is written in this case as follows ... 

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