From Intermolecular Potentials to the Spectra of van der Waals Molecules, and Vice Versa

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We present quantum mechanical calculations of the collision-induced absorption spectra of nitrogen molecules, using ab initio dipole moment and potential energy surfaces. Collision-induced spectra are first calculated using the isotropic interaction approximation. Then, we improve upon these results by considering the full anisotropic interaction potential. We also develop the computationally less expensive coupled-states approximation for calculating collision-induced spectra and validate this approximation by comparing the results to numerically exact close-coupling calculations for low energies. Angular localization of the scattering wave functions due to anisotropic interactions affects the line strength at low energies by two orders of magnitude. The effect of anisotropy decreases at higher energy, which validates the isotropic interaction approximation as a high-temperature approximation for calculating collision-induced spectra. Agreement with experimental data is reasonable in the isotropic interaction approximation, and improves when the full anisotropic potential is considered. Calculated absorption coefficients are tabulated for application in atmospheric modeling. C 2015 AIP Publishing LLC. [http://dx

Section: B Coupled-states Approximationmentioning

confidence: 99%

“…To exploit the body-fixed projection, K, of the total angular momentum as a good quantum number, the calculation should be performed in a body-fixed frame. Here, the primitive angular basis functions are defined by 24 …”

Section: B Coupled-states Approximationmentioning

confidence: 99%

Quantum mechanical calculation of the collision-induced absorption spectra of N2–N2 with anisotropic interactions

Karman

Miliordos

Hunt

et al. 2015

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“…The method to compute the intermolecular rovibrational states on the 5D intermolecular potential surface is based on a general formalism 51 developed for weakly bound dimer molecular complexes with large amplitude internal motion such as ammonia [52][53][54] and water 9, 51, 55-57 dimer. For details on the Hamiltonian, body-fixed coordinates, etc., the reader is referred to previous work.…”

Section: B Bound and Quasi-bound State Calculationsmentioning

confidence: 99%

Overtone vibrational spectroscopy in H2-H2O complexes: A combined high level theoretical ab initio, dynamical and experimental study

Ziemkiewicz

Pluetzer

Nesbitt

et al. 2012

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First results are reported on overtone (v OH = 2 ← 0) spectroscopy of weakly bound H 2 -H 2 O complexes in a slit supersonic jet, based on a novel combination of (i) vibrationally mediated predissociation of H 2 -H 2 O, followed by (ii) UV photodissociation of the resulting H 2 O, and (iii) UV laser induced fluorescence on the nascent OH radical. In addition, intermolecular dynamical calculations are performed in full 5D on the recent ab initio intermolecular potential of Valiron et al. [J. Chem. Phys. 129, 134306 (2008)] in order to further elucidate the identity of the infrared transitions detected. Excellent agreement is achieved between experimental and theoretical spectral predictions for the most strongly bound van der Waals complex consisting of ortho (I = 1) H 2 and ortho (I = 1) H 2 O (oH 2 -oH 2 O). Specifically, two distinct bands are seen in the oH 2 -oH 2 O spectrum, corresponding to internal rotor states in the upper vibrational manifold of and rotational character. However, none of the three other possible nuclear spin modifications (pH 2 -oH 2 O, pH 2 -pH 2 O, or oH 2 -pH 2 O) are observed above current signal to noise level, which for the pH 2 complexes is argued to arise from displacement by oH 2 in the expansion mixture to preferentially form the more strongly bound species. Direct measurement of oH 2 -oH 2 O vibrational predissociation in the time domain reveals lifetimes of 15(2) ns and <5(2) ns for the and states, respectively. Theoretical calculations permit the results to be interpreted in terms of near resonant energy levels and intermolecular alignment of the H 2 and H 2 O wavefunctions, providing insight into predissociation dynamical pathways from these metastable levels.

“…In an effort to avoid the isomorphic Hamiltonian in that case alternative derivations were presented, one starting with Cartesian coordinates and applying the chain rule 27 and one employing the Podolsky form of the Laplacian. 28 Both derivations require a somewhat ad hoc rewriting of the Hamiltonian in terms of angular momentum operators to arrive at the familiar results and electron spin was not considered.…”

Section: Appendix: Basis Functions and Rotational Hamiltonianmentioning

confidence: 99%

Reassignment of the O2 spectrum just below dissociation threshold based on ab initio calculations

Vroonhoven

Groenenboom

2002

Vibrational Herzberg bands of the O 2 molecule just below its first O( 3 P)ϩO( 3 P) dissociation limit are since long-known to be perturbed. Jenouvrier et al. ͓J. Mol. Spectrosc. 198, 136 ͑1999͔͒ assigned the cause of the perturbations to five vibrational levels supported by the shallow minimum in the 1 3 ⌸ u potential energy curve around 5.5a 0 . Using ab initio potential energy curves and spin-orbit couplings from previous work ͓J. Chem. Phys. 116, 1954 ͑2002͔͒ we present a full quantum calculation of all ungerade rotation-vibration-electronic states of oxygen just below the dissociation threshold, through a total angular momentum quantum number of Jϭ19. This calculation shows that the original assignment, based on a Hund's case ͑a͒ model of a regular 1 3 ⌸ u multiplet was not correct. Based on our calculation we present a new assignment of the perturbing states: 1 3 ⌸ u,⍀ϭ2 (vϭ0͒, 1 3 ⌸ u,1 ͑0͒, 1 3 ⌸ u,2 ͑1͒, 1 3 ⌸ u,1 ͑1͒, and 1 3 ⌸ u,0 Ϫ͑0͒ in order of ascending term values. We show the new assignment to be consistent with experimental data and we also propose new spectroscopic parameters for the perturbing states.