Herbert M. Pickett

Vibrational Spectra and Potential Functions of Cyclohexane and Related Oxanes

The vibrational spectra of cyclohexane, s‐trioxane, p‐dioxane, m‐dioxane, and tetrahydropyran and a number of their deuterated derivatives are re‐examined. Particular attention is paid to the low‐frequency modes. A number of low‐frequency difference bands and some hot bands are observed and assigned. Complete normal‐coordinate analyses are carried out for all the molecules. It is concluded that the six ring bending modes contain little contribution from other valence coordinates. A potential function for ring bending is then developed using the vibrational frequencies and the available information on molecular geometries. A onefold term in the torsional part of the potential is found to be necessary. The final potential function gives an excellent fit to the frequencies of the lowest‐frequency modes and to the geometries of the molecules considered. This potential function should be useful in conformational analysis.

General rotational relaxation matrix: Its properties, M dependence, and relation to experiment

A general rotational relaxation matrix, R, is introduced which governs relaxation among density matrix elements. A definition of R in terms of the scattering S matrix is made which has the properties of conservation of mass and detailed balance at equilibrium. The relation between R and S shows that the only nonzero elements of R are those which connect density matrix elements with approximately the same time dependence. Using only spatial invariance of the S matrix, the dependence of R on M, the space projection quantum number for rotational angular momentum, is found to lead to important information about the qualitative physical nature of collisions. Linewidth experiments, saturation experiments, and double resonance experiments are discussed in terms of what parts of R they measure and how they might yield information about the M dependence of R.

Thermodynamics of Linear Molecules at High Temperature: C3O2 and C5

In this paper we derive equations for the classical partition function of a linear molecule, taking account of anharmonicity and rotation–vibration interaction. We calculate the thermodynamic properties of C3O2 and C5 using a potential suggested by Morino, Kuchitsu, and Tanimoto. This potential, as well as a number of others, gives good agreement with the measured value of S°230 for C3O2 of McDougall and Kilpatrick.