Octupole Term Research Articles

Thermodynamic perturbation theory for simple polar fluids. II

The study of polar fluids begun in a previous paper is continued. Calculations for the Stockmayer potential are extended to include the term of order μ6, where μ is the dipole moment. The effects of higher-order terms are then approximated by means of a simple Padé extrapolation procedure, and the liquid-gas coexistence curve is located in this approximation. An orientation-independent but temperature-dependent potential that is thermodynamically equivalent to an arbitrary orientation-dependent potential is introduced and used to assess the lowest-order thermodynamic effects that result from the presence of quadrupole and octupole terms in the pair-potential. Several values of quadrupole and octupole moments representative of a dipolar molecule (HCl) as well as linear molecules (N2, O2 and CO2, for which μ=0) are considered.

A covariant theory of the photodisintegration of the deuteron — II

The calculation of the process γ+d → n+p is made in the framework of a covariant theory. There are twelve invariant amplitudes; they are related to helicity amplitudes and then to multipole amplitudes. A general formula is written explicitly for the calculation of any multipole amplitude from the twelve invariant amplitudes. The Born terms are derived and are then modified in order to take account of deuteron structure; this is done by using n-p-d vertex functions depending on the transfer. In I, we calculate the corresponding cross-section as well as the 10 dipole and 12 quadrupole amplitudes. It is shown that the octupole terms are not completely negligible for incident photon energies of about 100 MeV. The theory is equivalent in the low-energy limit to the usual nonrelativistic theory based upon Siegert’s theorem and excluding final-state interactions, but some of the multipole amplitudes seem to be affected by relativistic corrections for energies of order 100 MeV. Comparison with experiment shows very good agreement in view of the approximations made. In II, the final-state interaction for cross-section and polarization will be treated by means of dispersion relations, using the experimental nucleon-nucleon phase shifts.