Spectroscopic signatures of nonrigidity: Algebraic analyses of infrared and Raman transitions in nonrigid species

An algebraic scheme is proposed to explore the influence of nonrigidity upon spectroscopic (infrared/Raman) transitions. Application of this approach to large amplitude bending motion relies upon a Hamiltonian that embodies both rigidly-linear and rigidly-bent behavior, with the attendant U(3) dynamical algebra uniformly describing all pertinent operators. The bending mode supported by the quasilinear carbon trimer (C3) is investigated, yielding algebraic predictions for vibrational energy level patterns and infrared transition matrix elements that are in reasonable accord with their ab initio counterparts. A coherent state formalism is employed to extract dependence of potential energy and dipole moment functions on C3 bending coordinate.