Contents vii

§37. Physical meaning of the solutions ψ1 and ψ2 164

§38. Scattering by a rectangular barrier 167

§39. Scattering by a potential center 169

§40. Motion of wave packets in a central force field 175

§41. The integral equation of scattering theory 181

§42. Derivation of a formula for the cross-section 183

§43. Abstract scattering theory 188

§44. Properties of commuting operators 197

§45. Representation of the state space with respect to a

complete set of observables 201

§46. Spin 203

§47. Spin of a system of two electrons 208

§48. Systems of many particles. The identity principle 212

§49. Symmetry of the coordinate wave functions of a system

of two electrons. The helium atom 215

§50. Multi-electronatoms. One-electronapproximation 217

§51. The self-consistent field equations 223

§52. Mendeleev’s periodic system of the elements 226

Appendix: Lagrangian Formulation of Classical Mechanics 231