29pC01
窒素・酸素プラズマ中の中性分子・分子イオンの回転温度差
Difference in Rotational Temperature between Neutral Molecules
and Molecular Ions in N2/O2 Plasmas川野泰和1), 根津 篤2), 3), 松浦治明3)、赤塚 洋1), 3)
Hirokazu Kawano, Atsushi Nezu, Haruaki Matsuura and Hiroshi Akatsuka
1) 東工大・院・総理工, 2) 東工大・技術部, 3) 東工大・原子炉研Tokyo Institute of Technology
For a microwave discharge nitrogen plasma withits discharge pressure about 1 Torr, we found that therotational temperature Tr of the first negative system(1NS) of N2+ B 2Σu+ state is about 50 % times higherthan that of the second positive system (2PS) of N2 C
3
Πu state, as shown in Fig. 1 by OES measurement. For
2PS, we found 0.07 ≤ Tr [eV] ≤ 0.15, which isconsidered to be reasonable as an approximate value tothe gas translational temperature [1]. On the other hand,
the rotational temperature of 1NS is higher than that of2PS, found to be about 0.13 – 0.34 eV. It is consideredthat this is partly because most of the excitedmolecular ions are generated by the electron impact
from the ground state of ion, not of neutral molecule,where the electron temperature ranges from 2 to 4 eV
and the electron density from 1 × 1011 to 1 × 1012 cm–3[2]. Therefore, under the present discharge conditions,the rotational temperature could have a component thatis originated from the ions N2+. It indicates that therotational temperature of 1NS has some information on
ion temperature if the rotational motion of ions isequilibrated with their translational motion.
Meanwhile, Fig. 2 shows that the rotationaltemperature of 1NS of O2+ b 4Σg– state is almost thesame as that of atmospheric absorption band (A-band)of O2 b 1Σg+ state [3]. The electron temperature anddensity are almost the same with those of the nitrogenplasma. Consequently, we consider that O2+ b 4Σg– stateis mostly produced from the electron impact from theground state (X state) of O2+ ion. However, theFig. 1. Rotational temperature of 2PS band of N2
and that of 1NS band of N2+ of N2 plasma
depicted in Ref. [1].

Fig. 2. Rotational temperature of A-band of O2
and that of 1NS of O2+ of O2 plasma in Ref. [3].

rotational temperature is almost the same with that ofneutral O2 b 1Σg+ state, which is quite different from N2
plasma. Now we consider that the rotationaltemperature of the ground state of O2+ ion, that is, O2+
X 2Σg+ state should be much higher than that of the O2+b 4Σg– state due to the difference in the intermoleculardistance R, where that of the b state Rb =1.2797 Å ismuch larger than that of the ground state, RX = 1.1171
Å. The angular momentum of both X and b states arealmost conserved before and after the electron impact
excitation due to a small mass of an electron. Therefore,
the rotational temperature of the X state Tr(X) of O2+
ion should be estimated as Tr(X) ~ Tr(b) × (Rb/RX)2 =1.32 × Tr(b). This value, in some sense, gives a similar
result with that of nitrogen plasma, where theintermolecular distance of both B and X states of N2+
ion is almost the same. Consequently, it is consideredthat the ground-state molecular ion has higher
rotational temperature than neutral molecule, both fornitrogen and oxygen discharge plasmas under thepresent discharge conditions. We should further study
the reason why molecular ions have higher rotationaltemperature than neutral molecules.
[1] T. Sakamoto, H. Matsuura and H. Akatsuka: J. Appl.
Phys., 101, 023307 (2007).
[2] H. Kawano, A. Nezu, H. Matsuura and H. Akatsuka:
Abst. 8th EU-Jpn. Joint Symp. Plasma Proc. (JSPP2012) P07(2012).
[3] H. Akatsuka, K. Naoi and H. Matsuura: Papers Tech.
Meeting Plasma Sci. Technol & Pulsed Power Technol., IEE
Jpn., PST-11-95, PPT-11-96, pp. 21 – 26 (2011).