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Rotational spectra of methane and deuterated methane in helium
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10.1063/1.3396002
/content/aip/journal/jcp/132/17/10.1063/1.3396002
http://aip.metastore.ingenta.com/content/aip/journal/jcp/132/17/10.1063/1.3396002

Figures

Image of FIG. 1.
FIG. 1.

Pair distribution function in the molecular frame between and in bulk . Color maps of are shown in two perpendicular planar cuts. The top panel shows the DMC result with rotation correctly taken into account, while for the bottom panel the rotational motion was artificially frozen, i.e., was treated as a spherical rotor with infinite moment of inertia.

Image of FIG. 2.
FIG. 2.

The tetrahedral expansion coefficients of the pair distribution function between and bulk (in the frame), as defined in the Appendix B. The spherical average of , i.e., , is clearly the largest contribution, but as noted in the text, this does not contribute to the rotational self-energy . The dominant contribution to is therefore .

Image of FIG. 3.
FIG. 3.

Spectra for dipole transition (bottom) and quadrupole transition (middle: E symmetry; top: symmetry) for . Transitions that are not homogeneously broadened due to rotational relaxation ( and the main peak of , E symmetry) appear as sharp lines. We have broadened these transitions by an artificial imaginary part (dashed lines), see text.

Image of FIG. 4.
FIG. 4.

Spectra for dipole transition (bottom) and quadrupole transition (middle: E symmetry; top: symmetry) for . Transitions that are not homogeneously broadened due to rotational relaxation ( and the main peak of , E symmetry) appear as sharp lines. We have broadened these transitions by an artificial imaginary part (dashed lines), see text.

Image of FIG. 5.
FIG. 5.

Left: schematic of the rovibrational energy levels in the ground and first excited vibrational states of the mode of together with the corresponding spectroscopic transitions. Right: schematic of the rotational energy levels and corresponding transitions in the ground vibrational state that derive from the and rotational levels calculated in this work.

Image of FIG. 6.
FIG. 6.

The tetrahedral expansion coefficients (top panel) and (bottom panel) for and in bulk for obtained by DMC simulation. , the dominant contribution to the reduction in rotational energies, is about twice as large for (dotted line) as for (solid line).

Image of FIG. 7.
FIG. 7.

Reduction in lowest rotational excitation energy for and as a function of the relative effective mass , where this is treated as a variable parameter.

Tables

Generic image for table
Table I.

Rotational energies , , and for and in obtained from CBF-DMC calculations. The square brackets indicate whether the MP4 or VB potential of Ref. 20 for the methane-helium interaction has been used. All energies are given in .

Generic image for table
Table II.

Rotational constants , , and obtained from the rotational energies for of given in Table I. Also shown are the experimental values of rotational constant (vibrational ground state) and distortion constant from Refs. 22 and 23 and experimental values from Ref. 24. Square brackets indicate whether the MP4 or VB potential for the methane-helium interaction has been used in the calculations. All energies are given in . Reductions in relative to the gas phase value are shown in parentheses.

Generic image for table
Table III.

For both methane-helium interaction potentials, the rigid rotor estimates are tabulated for and , as well as the changes with respect to the gas phase value (, (Ref. 17)), , and of the effective moment of inertia . We also tabulate the relative reduction for and , which scales roughly linearly with the respective gas phase moment of inertia . Energies are given in , moments of inertia are given in .

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/content/aip/journal/jcp/132/17/10.1063/1.3396002
2010-05-05
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Rotational spectra of methane and deuterated methane in helium
http://aip.metastore.ingenta.com/content/aip/journal/jcp/132/17/10.1063/1.3396002
10.1063/1.3396002
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