22P086-R
Plasma Spectroscopy of Sucrose Triboluminescence in Air and Hydrogen gas
空気や水素ガス中でのショ糖結晶の破壊に伴う発光のプラズマ分光計測
Yutaro Koike, Keisuke Fujii, Hiromichi Azuma, Yuki Oyama, Taiichi Shikamaand Masahiro Hasuo
小池祐太郎，藤井恵介，東裕通，大山勇己，四竈泰一，蓮尾昌裕
Graduate School of Engineering, Kyoto University
Yoshidahonmachi, Sakyo-ku, Kyoto 606-8501, Japan
京都大学大学院工学研究科 〒606-8501 京都市左京区吉田本町
We have observed emission spectra of triboluminescence caused by fracturing a sucrose crystal in air or ahydrogen gas. For the air experiment, we measure and analyze band spectra of the nitrogen molecule
second positive systems to estimate rotational and vibrational temperatures of nitrogen molecules. For thehydrogen gas experiment, we measure and analyze line widths of hydrogen Hα and Hβ emissions toestimate atom and electron densities.

1. Introduction
Luminescence produced by crystal fracture iscalled triboluminescence. Triboluminescence of asucrose crystal is well known and has been
observed for hundreds of years. Triboluminescenceis thought to be caused by a gas discharge between
a crystal crack. The mechanism of the discharge
generation is, however, not fully clarified [1].
In an air discharge, it is known that an emission
band of the nitrogen molecule second positivesystems is observed [2]. From the shape analysis of
the band spectra, rotational and vibrationaltemperatures of nitrogen molecules have been
estimated [3]. The rotational temperature is known
to be close to the air temperature [4]. On the other
hand, in a hydrogen discharge, atom and electron
densities have been estimated from the Lorentz
width of the Balmer emission lines [5,6].
In this work, we observe and analyze highresolution spectra of triboluminescence generated
when a sucrose crystal is fractured in air or in ahydrogen gas to estimate such plasma parameters.
2. Experiment
Figure 1 shows a schematic illustration of theexperimental set-up. The apparatus is composed of
fracturing and spectroscopic systems. In thefracturing system, we fracture a sucrose crystal bydropping a brass weight of 1.3 kg from 30 cm
above the crystal. The system is connected to open
air or a hydrogen gas cylinder from one side and toa vacuum pump from the other side for the purposesof exchanging the gas and adjusting its pressure.

We focus the triboluminescence on the entrance
slit of a spectrometer (Jobin Ybon, HR640, focal
length: f = 640 mm, 2400 grooves/mm) with aquartz lens (f = 150 mm). We record the emission
spectra with an image intensified CCD camera(Roper Scientific, ICCD-576-LDS). We measure asingle spectrum for a single weight drop.

Fig. 1. A schematic illustration of the experimental
set-up.

In the air triboluminescence experiment, we set
the air pressure to be 0.0026, 0.026, 0.13 and 1.0
atm. We carry out 14 measurements for each airpressure.
In the hydrogen triboluminescence experiment,
we also set the gas pressure to be 0.0026, 0.026,
0.13 and 1.0 atm. We observe Hα and Hβ emission
lines. We carry out 8 and 8 measurements for theHα and Hβ emissions, respectively, for a single gaspressure.
3. Results and discussion
Figure 2 (a) shows an example of the observednitrogen spectra at an air pressure of 1.0 atm. We fit
the observed spectrum by the calculation withadjustable parameters of the rotational andvibrational temperatures [3,7-9]. The fitting is done
for the results of 14 measurements at a single airpressure. We calculate the mean value of thetemperature and estimate the error bar as thestandard deviation from the 14 experiments. Figs. 2(b) and (c) show thus estimated temperatures as afunction of gas pressure.
The rotational temperature is about 400 K and its
pressure dependence is not clearly observed. The
vibrational temperatures at 0.026, 0.13 and 1.0 atm
are about 1000 K, and are within the error bars. The
vibrational temperature at 0.0026 atm is found to bemuch higher than the other cases.

mainly caused by atom collisions and Stark effect,
and that the electron temperature is 40000 K [10].
The width due to atom collisions is related to thehydrogen atom density, na [11], while that due toStark effect is related to the electron density, ne [12].
From these relations different for the Hα and Hβlines, we estimate na and ne to be about 3 x 1024 m-3
and about 4 x 1019 m-3, respectively.

Fig. 3. Examples of the observed (a-1) Hα and (b-1) Hβspectra at a hydrogen gas pressure of 0.026 atm. The
average of 8 spectra of the (a-2) Hα and (b-2) Hβ lines.
+ : data points. The lines are the fitted results.

Acknowledgments
This work was partly supported by Grant-in-Aidfor Scientific Research (B) (No.21340170).

Fig. 2. (a) An example of the observed spectra of thenitrogen molecule second positive system at an airpressure of 1.0 atm. + : data points. The line is the fittedresult. (b) Rotational and (c) vibrational temperatures ofnitrogen molecules as a function of the gas pressure.

For the experiment of the hydrogen
triboluminescence, we show the results only for
0.026 atm because the emission intensities were too
weak for the spectral shape to be analyzed at 0.13
and 1.0 atm and the spectra at 0.0026 and 0.026 atm
were similar to each other. Figs. 3 (a-1) and (b-1)
show examples of the observed Hα and Hβ spectra,
respectively, for a single weight drop. Since thescatter of the data point is large, we average over 8spectra to analyze the line profile. Figs. 3 (a-2) and(b-2) show the results for the Hα and Hβ lines,respectively.
We fit the spectra with a Voigt function toestimate the Lorentz width of the Hα and Hβ lines.
The fitted results are shown by the curves in Figs. 3(a-2) and (b-2). We assume that the Lorentz width isReferences[1] A.J. Walton: Adv. Phys. 26 (1977) 887.
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