The infrared spectra of the vapors of all cadmium and mercury halides were studied at low temperatures by matrix isolation. The spectra are classified into four absorption regions recorded in the 800–35-cm−1 range. The highest and lowest frequencies are assigned to the antisymmetric stretching mode and the doubly degenerate bending modes, respectively, of the MX2 molecules. The nature of the bonding in the molecule is discussed and statistically calculated entropy values are compared with corresponding values obtained from thermochemical measurements.

The polarized absorption and fluorescence spectra of single crystals of 2,2′-paracyclophane at 20°K were recorded in the region 3300–3100 Å. The spectra consist of narrow lines of which 87 could be measured in absorption and nine in emission. Single crystals having two different planes developed could be prepared sufficiently thin for measurements. The spectra obtained could be divided into two components, one characteristic of a transition moment parallel and the other perpendicular to the unique axis of the tetragonal crystal. These polarization directions are characteristic of molecular directions since in this case no Davydov splitting is to be expected in view of the high symmetry of the crystal. The absorption system is analyzed satisfactorily as representing the forbidden component of the benzene 1A1g→1B2u transition in the ``dimer'' molecule. A totally symmetric progression-forming frequency of 240 cm—1 is assigned as the intermoiety vibration. The appearance of a weak 0–0 transition is interpreted as due to a small-amplitude twist of the moieties relative to one another.

The absorption and circular dichroism spectra of trans-cyclooctene, α-pinene and β-pinene were measured in the gas phase in the vacuum ultraviolet. The absorptions were recorded to 110 nm and the CD spectra to 150 nm. Consistent assignments were made for these three ethylene chromophore molecules using the measured anisotropy factors (g = Δε/ε) to characterize transitions. Also, available theoretical work was used as a guide. In particular, magnetic dipole allowed transitions in the parent molecule, ethylene, have been characterized and assigned.

No abstract

The studies of the absorption and fluorescence spectra of single crystals of (2, 2)paracyclophane in the region 3300–3100 Å reported in a previous paper have been extended. Well-characterized samples with the (hk0) developed crystal plane were used. In absorption two distinct spectra were obtained in the two polarization components. The fluorescence was strongly polarized in one direction (parallel to the fourfold c axis) and represents the mirror image of the equally polarized absorption component. It was concluded that the observations prove conclusively that the differently polarized spectral components represent transitions to two different electronic states, with an energy difference of 369 cm−1. The lowest-energy transition certainly contains the 0–0 line and all available evidence supports the conclusion that also the second transition has allowed character. The only interpretation consistent with all observed features of the spectra is as follows. The two observed states are the gerade dimer states (B2g and B3g in D2h) being the out-of-phase combinations of the B2u and B1u benzene moiety states. The transitions have allowed character due to a torsional distortion of the molecule in the excited state. The interpretation is fully consistent with theoretical energy calculations.