Methane and Deuteromethane. New approaches to standard theory and experiments (original) (raw)
Related papers
2019
We report the correction factors for centrifugal distortion in Raman intensities for pure rotation (O0- and S0-branch) and vibration–rotation (O1- and S1-branch) transitions in the ground electronic state of H<sub>2</sub>, HD and D2. These factors are presented for 52 selected excitation wavelengths and for the initial rotational states, J=2−21. This data is useful in applications of intensity calibration of spectrometers and the spectroscopy of flames. The classical treatment of centrifugal distortion involved the expansion of polarisability anisotropy (<i>γ</i>) over the internuclear distance, while assuming the diatomic molecule behaves as a harmonic oscillator. Here, this approximation of polarisability invariants as a Taylor series expansion is tested, revealing that truncation up to the second-order derivatives of mean polarisability (α¯) and polarisability anisotropy (<i>γ</i>) gives faithful representations, yielding accurate expectation v...
Theory of vibrational and rotational excitation of polyatomic molecules
Physics Reports, 1989
A review is given of the theory of vibrational-rotational excitation of polyatomic molecules, based on the quasiclassical uniform representation of the scattering amplitude in action-angle variables. Models of molecules and interaction potentials are discussed. The relation of the quasiclassical approach to the quantum treatment and different approximations are illustrated. Analytical representations for cross sections and rate constants are given and the results of calculations are compared to experimental and more refined theoretical data.
Ab initio calculation of the rotational spectrum of methane vibrational ground state
The Journal of Chemical Physics, 2012
The first article of this series has introduced an alternative perturbation scheme to find approximate solutions of the spectral problem for the rotation-vibration molecular Hamiltonian. The convergence of our method for the methane vibrational ground state rotational energy levels was quicker than that of the traditional method, as expected, and our predictions were quantitative. In this second article, we study the convergence of the calculation ab initio of effective dipole moments for methane within the same theoretical frame. The first order of perturbation when applied to the electric dipole moment operator of a spherical top gives the expression used in previous spectroscopic studies. Higher orders of perturbation give corrections corresponding to higher centrifugal distorsion contributions and are calculated accurately for the first time. Two potential energy surfaces of the literature have been used for solving the anharmonic vibrational problem by means Preprint submitted to J. Chem. Phys.
Fundamentals of Rotation-Vibration Spectra
Handbook of High-resolution Spectroscopy, 2011
We provide a survey of fundamental aspects of rotation-vibration spectra. A basic understanding of the concepts is obtained from a detailed discussion of rotation-vibration spectra of diatomic molecules with only one vibrational degree of freedom. This includes approximate and exact separation of rotation and vibration, effective spectroscopic constants, the effects of nuclear spin and statistics, and transition probabilities derived from the form of the electric dipole moment function. The underlying assumptions and accuracy of the determination of molecular structure from spectra are discussed. Polyatomic molecules show many interacting vibrational degrees of freedom. Energy levels and spectra are discussed on the basis of normal coordinates and effective Hamiltonians of interacting levels in Fermi resonance, and in more complex resonance polyads arising from anharmonic potential functions. The resulting time-dependent dynamics of intramolecular energy flow is introduced as well. Effective Hamiltonians for interacting rotation-vibration levels are derived and applied to the practical treatment of complex spectra. Currently available computer programs aiding assignment and analysis are outlined.
Molecular Physics, 2019
We report the correction factors for centrifugal distortion in Raman intensities for pure rotation (O0-and S0-branch) and vibration-rotation (O1-and S1-branch) transitions in the ground electronic state of H 2 , HD and D 2. These factors are presented for 52 selected excitation wavelengths and for the initial rotational states, J = 2 − 21. This data is useful in applications of intensity calibration of spectrometers and the spectroscopy of flames. The classical treatment of centrifugal distortion involved the expansion of polarisability anisotropy (γ) over the internuclear distance, while assuming the diatomic molecule behaves as a harmonic oscillator. Here, this approximation of polarisability invariants as a Taylor series expansion is tested, revealing that truncation up to the second-order derivatives of mean polarisability (ᾱ) and polarisability anisotropy (γ) gives faithful representations, yielding accurate expectation values with error < 0.2%, for the ground rovibrational state and for the fundamental transition.
Inversion-vibration energies of CH3− and adiabatic electron affinity of CH3
Journal of Molecular Spectroscopy, 1991
The inversion potential of the X'A, electronic ground state of the methyl anion CH; is investigated at the SCF/single-reference configuration interaction (SCF/SR-CI) and at the completeactive-space SCF/multireference CI (CASSCF/MR-CI) levels of theory employing large Gaussian basis sets augmented by diffuse functions to represent the weakly bound carbon lone-pair electrons. These calculations, together with the corresponding out-of-plane bending potential of the CH3 radical, demonstrate that the Born-Oppenheimer separation of the electronic and nuclear motions becomes invalid when moving along the inversion potential of CH;. In order to treat the nuclear dynamics of the autodetaching resonant CH; ion by conventional methods, a quasi-diabatic representation of the full-dimensional potential energy hypennuface is evaluated applying standard SCF/SR-CI calculations. From the resulting anharmonic potential function the vibration-rotation energies of the CH; and CD; isotopic variants are calculated using an improved version of the nonrigid inverter Hamiltonian approximation. Combining the present results with the previously determined vibrational potential function for the methyl radical CHj, the different stabilities of the CH; and CD; isotopes against autodetachment are discussed in terms of effective potentials for the inversion motion and the adiabatic electron affinity of CH3 is determined as EA = 0.09 eV close to the experimental value of 0.08 + 0.03 eV. The photoelectron spectrum of CH; is calculated within the Franck-Condon approximation in good agreement with the experimental spectrum. Present predictions of the lower inversion-vibration energy levels and the corresponding rotation constants of the CH; ion are expected to be reliable. o 1991 Academic press. IIIC.
Frequency shifts of vibrational and rotational states of dilute<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline">mml:mrowmml:msubmml:mrow<mml:mi mathvariant="normal">Hmml:mrowmml:mn2,<mml:ma...
Physical review, 1986
The frequency shifts of the vibrational and rotational transitions of H2, D2, and HD molecules trapped in solid Ar are calculated at zero temperature and at pressures 0 & P & 373 kbar. It is found that the pure vibrational and rotational-vibrational transition frequencies are strongly red-shifted in the solid at P =0, compared to gas-phase values, and the agreement with Raman scattering measurements is generally good. The calculated pure rotational transitions also show a small red shift at P =0 in the solid and are in generally good agreement with the measurements of Jodl and Bier, but less so with those of Prochaska and Andrews, who, except for D2(Ar), measure small blue shifts. The calculated local-mode frequencies of the impurity molecules in the solid at P =0 are also in good agreement with experiment, especially when thermal corrections are considered. VA'th increasing pressure all transition frequencies and the local-mode frequencies are strongly blue-shifted with respect to P =0 solid values.