On the rotational constants of floppy molecules

Quantum Monte Carlo studies of the structure and spectroscopy of NenOH (Ã 2Σ+, n=1–4) van der Waals complexes

“…For the purposes of the calculation of rotational constants, the hydrogen atom is unimportant, and we can treat Ne 2 OH as a triatomic system, where OH has been replaced by a structureless particle with the mass of OH. Further, based on the masses and geometry of Ne 2 OH, the B-axis will be perpendicular to R com in the geometric embedding, while the angle between the A-axis and R com in the Eckart embedding, A , is given by 29,39 tan A ϭ Ne-Ne r e r sin͑Ϫ e ͒ Ne 2 -OH R com,e R com ϩ Ne-Ne r e r cos͑Ϫ e ͒ , ͑5͒…”

“…27,28 The importance of using the Eckart conditions to define the inertial axes in calculations of the rotational constants of floppy molecules has been recognized by Hutson and co-workers. 29 While the Eckart conditions have been used in several earlier DMC studies by Buch and co-workers, 30,31 the numerical algorithms that were used to implement the Eckart conditions have not been fully described.…”

Comparison of rotational energies and rigidity of OCS–para-H2 and OCS–4He complexes

“…[14,35]) calculated in the Eckart frame (x, y, z). We use the definition of of the Eckart frame axes given in Ref.…”

“…The explicit expressions for A, B, C, and D are given in Ref. [14]. Rotational energies are then obtained by expanding H eff rot in the symmetric rotor basis and diagonalizing the matrix.…”

“…We described the clamped coordinate quasiadiabatic approximation of Quack and Suhm [12], a modification of it which incorporates the Eckart condition [13] for semi-rigid complexes, and a perturbative calculation of rotational constants following Ref. [14]. In section 4, we compare these results with the exact bound state energies determined by the program BOUND [15].…”