A theoretical rotationally resolved infrared spectrum for H2O+ (X 2B1)

Abstract

Three-dimensional potential energy and electric dipole moment functions for the electronic ground state of H2O+ have been calculated from highly correlated multiconfiguration reference configuration interaction (MRCI) electronic wave functions. The analytic representations of these functions have been used in vibrational and perturbational calculations of the rovibrational absorption spectrum of H2O+. The quartic force fields in normal coordinates have been employed in the evaluation of the equilibrium spectroscopic constants in H2O+, D2O+, and HDO+ by perturbation theory. The equilibrium structure, vibrational band origins, centrifugal distortion constants and rotational energy levels agree very well with the available experimental data. Absolute vibrational band intensities have been calculated from the dipole moment functions and are compared with theoretical integrated band intensities. The radiative lifetimes of excited vibrational states exhibit mode specific variations. The rotationally resolved room temperature absorption spectra have been evaluated ab initio for the pure rotational and the ν2, 2ν2, ν1, ν3, and 3ν2 transitions. The rovibrational electric dipole transition matrix elements and absolute line intensities are given for the most intense transitions. These data take full account of anharmonicity effects and vibration–rotation coupling.

Detection of interstellar oxidaniumyl: Abundant H2O+towards the star-forming regions DR21, Sgr B2, and NGC6334

“…The H 2 O + cation is a radical with a 2 B 1 electronic ground state and bond lengths and angle slightly larger than H 2 O. Quantumchemical calculations (Weis et al 1989) yield a ground-state dipole moment of 2.4 D. The B 1 symmetry of the ground electronic state leads to a reversal of the ortho and para levels relative to water.…”

Excited OH+, H2O+, and H3O+in NGC 4418 and Arp 220

“…HIFI observations of the N = 1 10 −1 01 transition frequencies above 600 GHz toward Sgr B2(M) reported by Schilke et al (2010) are compatible with the transition frequencies in the CDMS, although these lines lie outside our accessible frequency range. A ground state dipole moment of 2.398 D was calculated ab initio by Weis et al (1989).…”

Ab Initio Ro-Vibrational Structure of the C2? Isotopes of H2O+

“…The calculations use the discrete ab initio potential energy surface of Weis et al (1989). Where comparisons can be made, the assignment of the vibrational states is in excellent agreement with experiment and with the ab initio variational calculation of Weis et al, who utilised a different force field and an internal coordinate nuclear Hamiltonian (instead of the Eckart-Watson Hamiltonian).…”

“…More pertinent to this study is the work of Weis et al (1989), who have theoretically resolved the infrared spectrum of H20+, D20+ and HDO+ using the 'complete' approach. That is, they have calculated a multiconfiguration reference configuration interaction (MRCI) discrete potential energy surface and embedded an analytical representation of it in an internal coordinate ro-vibrational Hamiltonian, which they have variationally solved using basis functions constructed from Morse, harmonic oscillator and associate Legendre functions.…”

“…Although we have employed the discrete MRCI potential of Weis et al (1989), we have utilised a different force field embedded within the Eckart-Watson Hamiltonian and have used different ro-vibrational trial functions in our variational solution. Nevertheless, we will show that our t coordinate solution produces ro-vibrational eigenenergies in excellent agreement with the internal coordinate solution of Weis et al (1989) and with experiment for the isotopes (where comparison can be made). Furthermore, we report theoretically determined ro-vibrational states for the C2v isotopes, where no experimental or ab initio data are currently available.…”