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Density effect on infrared spectrum for supercritical water in the low- and medium-density region studied by molecular dynamics simulation
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10.1063/1.4767352
/content/aip/journal/jcp/137/19/10.1063/1.4767352
http://aip.metastore.ingenta.com/content/aip/journal/jcp/137/19/10.1063/1.4767352

Figures

Image of FIG. 1.
FIG. 1.

Comparison of the spectrum of the dipole time correlation function calculated at 400 °C with the experimental IR spectrum. The experimental data in (a) by Tassaing et al. (Ref. 6) are taken at 380 °C with 0.009 g cm−3 and those by Vigasin et al. (Ref. 7) at 377 °C with 0.0105 g cm−3. In (b), the data by Tassaing et al. are at 380 °C with 0.04 g cm−3 and those by Vigasin et al. are at 377 °C with 0.0405 g cm−3. The calculated spectrum is shifted by 50 cm−1 to the higher frequency for comparison of the line shape to the experimental one.

Image of FIG. 2.
FIG. 2.

The O−H stretch spectrum calculated at 400 °C for an isolated single molecule as the reference of the zero-density limit. The spectra are calculated without and with the rotational degree of freedom from (a) the dipole and (b) hydrogen velocity time correlation function. The spectrum calculated at 1200 °C with rotations allowed are also included.

Image of FIG. 3.
FIG. 3.

The O−H spectrum of the dipole time correlation function in the low-density range of 0.01–0.2 g cm−3 and (a) at 400 °C and (b) at 1200 °C.

Image of FIG. 4.
FIG. 4.

The density dependence of the reorientational correlation times τ 1R and τ 2R for supercritical water calculated at 400 °C for the SPC/Fw model.

Image of FIG. 5.
FIG. 5.

(a) The probability P n HB of finding a molecule with n hydrogen bonds for the SPC/Fw water at 400 °C. (b) The normalized autocorrelation function of the hydrogen velocity, C vH(t) = ⟨v H(0)· v H(t)⟩/⟨v H(0)· v H(0)⟩ at 400 °C and at 0.01 g cm−3 and (c) C vH(t) conditioned with n HB = 0 and (d) that conditioned with n HB = 1. (e) The dependence of the O−H stretch mode on the number of hydrogen bonds n HB at 400 °C and at 0.01 g cm−3. The spectra are the Fourier transform of the n HB-conditioned C vH(t) shown in (c) and (d).

Image of FIG. 6.
FIG. 6.

The comparison of the O−H stretch mode of the hydrogen velocity spectrum for the same n HB at different bulk densities.

Image of FIG. 7.
FIG. 7.

The shift of the O−H stretch mode calculated for MD simulation and the one observed by Raman spectroscopy (Ref. 46) at 400 °C and at 0.01–0.6 g cm−3.

Image of FIG. 8.
FIG. 8.

Density and temperature dependencies of (a) O−H bond length r OH, (b) H−O−H angle θ∠HOH, and (c) dipole moment μ for SPC/Fw water in supercritical states.

Image of FIG. 9.
FIG. 9.

The comparison of the experimental and calculated spectra of the O−H stretch mode in the ambient condition. The experimental data are taken from Ref. 48. For the calculated ones, the spectra at the ambient density of 1.0 g cm−3 at high temperatures of 200–1200 °C are also included.

Tables

Generic image for table
Table I.

The parameter values for the SPC/Fw model.27 Definitions of the constants are shown in Eqs. (1) and (2).

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/content/aip/journal/jcp/137/19/10.1063/1.4767352
2012-11-20
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Density effect on infrared spectrum for supercritical water in the low- and medium-density region studied by molecular dynamics simulation
http://aip.metastore.ingenta.com/content/aip/journal/jcp/137/19/10.1063/1.4767352
10.1063/1.4767352
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