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Spectroscopic studies of the phase transition in ammonia borane: Raman spectroscopy of single crystal as a function of temperature from
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10.1063/1.2820768
/content/aip/journal/jcp/128/3/10.1063/1.2820768
http://aip.metastore.ingenta.com/content/aip/journal/jcp/128/3/10.1063/1.2820768

Figures

Image of FIG. 1.
FIG. 1.

Comparison of the Raman spectra collected at , bottom, to the spectral harmonic density, a histogram with the number of modes predicted by the electronic structure calculation within a bin simulating intensity, middle, and the constant energy spectrum, or dynamics, at .

Image of FIG. 2.
FIG. 2.

(a) Raman spectra of the N–H stretching region collected as a function of temperature. At room temperature, the prominent peak at is the symmetric stretch with symmetry, the peak at is the asymmetric, peak, and the is unassigned. At , the asymmetric peak clearly has split into and modes and the symmetric peak has not as predicted by site symmetry. At lower temperature, each of these branches splits and a low frequency shoulder is resolved on the peak fulfilling the splitting predicted from the impact of the factor group. At , the arrows identify the contribution from isotope. (b) A graphical representation of the frequency shifts measured and mode appearance in the N–H stretching region collected as a function of temperature.

Image of FIG. 3.
FIG. 3.

Raman spectra of the B–H stretching region collected as a function of temperature. At room temperature, the prominent peak at is the symmetric stretch with symmetry, the asymmetric peak is poorly resolved at , and the peak at is unassigned. At , the symmetric peak splits into and components, whereas splitting of the peak remains poorly resolved due to broad peak widths and close spacing of peaks. At , arrows identify the contribution from isotope.

Image of FIG. 4.
FIG. 4.

Raman spectra of the deformation region collected as a function of temperature. At room temperature, the prominent peaks at 1357 and are the symmetry and asymmetric deformation modes, respectively. At , both modes split into two components, the asymmetric mode exhibiting site symmetry splitting, while the symmetric mode displays factor group splitting. At lower temperature, each of the and modes split as predicted by the factor group splitting.

Image of FIG. 5.
FIG. 5.

Raman spectra of the deformation and high frequency rocking region collected as a function of temperature. At room temperature, the prominent peaks at 1155 and are assigned to the and deformation modes. A weak broad peak at is an asymmetric rocking mode. At , both deformation modes split, the asymmetric mode exhibiting site symmetry splitting, while the symmetric mode displays factor group splitting. At lower temperature, each of the and modes split as predicted by the factor group splitting. The asymmetric rocking mode splits into three peaks, suggesting factor group splitting with two of the four peaks having coincidental splitting or low intensity.

Image of FIG. 6.
FIG. 6.

Raman spectra of the B–N symmetric stretch and low frequency rocking region collected as a function of temperature. The and isotopic splittings are clearly evident at 782 and in the room temperature spectra. A low frequency asymmetric rocking mode is evident at which splits into and modes at . At , weak shoulder peaks on B–N symmetric stretch are evident and the splits.

Tables

Generic image for table
Table I.

Factor group analysis of tetragonal , , .

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Table II.

Factor group analysis of orthorhombic , , .

Generic image for table
Table III.

Correlation between irreducible representations in and through .

Generic image for table
Table IV.

Tetragonal ammonia borane. st, stretch; d, deformation; ds, scissors; du, umbrella; r, rock; ov, overtone; dp, depolarized; p, polarized; no, not observed; and nr, not reported.

Generic image for table
Table V.

Orthorhombic ammonia borane. st, stretch; d, deformation; ds, scissors; du, umbrella; r, rock; ov, overtone; dp, depolarized; p, polarized; and no, not observed; INS, inelastic neutron scattering.

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/content/aip/journal/jcp/128/3/10.1063/1.2820768
2008-01-18
2014-04-17
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Spectroscopic studies of the phase transition in ammonia borane: Raman spectroscopy of single crystal NH3BH3 as a function of temperature from 88to330K
http://aip.metastore.ingenta.com/content/aip/journal/jcp/128/3/10.1063/1.2820768
10.1063/1.2820768
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