| We investigate the classical mechanics of diatomic and symmetric top molecules in tilted fields. These molecules exhibit regular, chaotic or mixed phase space depending on the tilt angle beta, the energy E, and the relative intensity of the fields o/Deltao. In the integrable collinear problem the projection of the angular momentum into the spatial z axis is a constant of motion, m, which allows us to use energy momentum diagrams to classify the motions of the rotor. For beta ≠ 0 the system is non-integrable showing mostly regular dynamics in the high-energy (free-rotor) and low-energy (pendular) limits; for energy near the tilted fields barrier the phase space is highly chaotic with degree of chaos increasing with beta between 0 and pi/2. Periodic orbits and bifurcation diagrams are obtained from symmetry lines and their iterations under the Poincare map. Some quantum eigenstates are localized near stable or unstable periodic orbits showing tori quantization or scarring respectively.; For asymmetric top molecules in parallel fields m is a constant of the motion and it is possible to define an effective potential Vm(theta, psi). In an E-m diagram the equilibrium solutions of Vm(theta, psi) are curves that enclose regions of qualitatively different accessible theta-psi configuration space; these regions can be used to classify the quantum eigenstates.; For plane rotors several primitive semiclassical methods are used to calculate the rotational excitation caused by laser pulses. In the case of plane rotors in electric fields we calculate energy spectra, orientation (⟨cos ϕ⟩), and alignment (⟨cos2 ϕ⟩), using the Herman-Kluk propagator in terms of periodic coherent states. For diatomic rotors in tilted fields, the HK propagator was used to calculate energy spectra with good agreement for high-energy and not very dense eigenspectra. Some steps are taken towards the development of HK-type propagator for rotational coherent states. |
