Variational ro–vibrational wave functions are calculated using an
Eckart?Watson Hamiltonian, which has embedded an ab initio
potential energy function. These wave functions,together with an ab initio
dipole moment function,are employed to predict transition energies and
absorption intensities. The radiative transition probability integrals are
determined using a novel adaptation of the
Harris–Engerholm–Gwinn integration scheme. The method
and solution algorithm yields results in excellent agreement with previously
determined experimental and theoretical electric dipole allowed transitions
for the 1 A 1 ground state of H
2 O. The method has also been applied to the
1 A 1 states of the helide analogs
of water, namely He 2 O 2+
and He 2 S 2+, in order to
predict their ro–vibrational transition energies and absorption
intensities, thereby facilitating their possible interstellar detection.