Infrared and ultraviolet spectroscopic studies have been conducted on the products of the vacuum‐ultraviolet photolysis of normal and isotopically substituted methyl chloride and methylene chloride isolated in argon and nitrogen matrices at 14°K. The cage effect has been found to inhibit halogen detachment processes in these systems. Infrared absorptions attributable to CCl, HCCl, and H2CCl and the 2800‐A ultraviolet absorption of CCl appear in the methyl chloride photolysis studies. Observation of a “negative anharmonicity” for the lowest‐frequency infrared absorption of H2CCl can be explained by postulating that the molecule is planar. The C–Cl stretching force constant of H2CCl is exceptionally high. The implications of (p–d)π bonding, which may account for the large C–Cl stretching force constant, are explored. An absorption near 2300 A behaves appropriately for assignment to a second electronic transition of CCl, providing support for the previous tentative assignment of a group of emission bands to such a transition. Photolysis of methylene chloride in a matrix environment leads principally to the stabilization of CCl2. A revised estimate of the force constants of CCl2 is given.

Matrix‐Isolation Study of the Vacuum‐Ultraviolet Photolysis of Methyl Chloride and Methylene Chloride. Infrared and Ultraviolet Spectra of the Free Radicals CCl, H2CCl, and CCl2

Diode laser spectroscopy of the CCl radical

Microwave spectroscopy of the CCl radical

Chemiluminescent reactions in diffusion flames of alkali metals with haloforms and carbon tetrahalides appear to provide examples of reactions in which essentially all of the exothermicity appears as vibration in a newly formed bond. A self‐consistent account of the intensity distributions in the flame spectra requires that, in CX4—K flames, both excited and unexcited carbon atoms participate in the reactions, C+CX→C2*+X, and that the X atoms be produced both in the ground and first excited states. Excited C atoms appear not to be produced in CHX3—K flames in appreciable concentrations. The excited C2 intensity distributions in emission are compatible with the bond dissociation energies, C–Cl=77 kcal, C–Br=66 kcal, and C–I=50 kcal, with uncertainties of about 4 kcal in each.

Chemiluminescence and Radical Reactions in Diffusion Flames of Alkali Metals with Organic Halides

The A 2Δ-X 2Π transition of CCl has been studied with the High Frequency Deflection (HFD) technique. Lifetimes were measured for the ν′ = 0, 1 and 2 vibrational levels of the A 2Δ state. A drastic shortening of the lifetime going from ν′ = 0 to ν′ = 1 indicated that a predissociation takes place. In order to obtain more information about this predissociation, potential energy curves were calculated with the CASSCF method and the contracted CI method for the bound X 2Π and A 2Δ states and several repulsive states. It was found that the dominating cause of the predissociation is a 2Π state going to the ground state dissociation products. Electronic matrix elements were roughly estimated and the bound-continuum vibrational overlap integrals were calculated. The A 2Δ-2Π crossing point was adjusted until satisfactory agreement was obtained between experimental and theoretical predissociation rates for ν′ = 1.

Theoretical and experimental studies of a new predissociation in the A 2Δ state of CCl

A rotational analysis of the 2780 A emission band obtained in a microwave discharge through CCl4 vapor and photographed on a 20-ft grating spectrograph shows that a 2Δi(b) → 2Πr(a) transition of the CCl radical is responsible, not 2Σ → 2Π(a) as reported by previous workers. Molecular constants are given for the combining states, as well as a vibrational analysis that identifies the 2780 A band as the (0–0) band.

R. D. Gordon

Papers

The emission spectrum of the cci radical