Optical absorption spectra and kinetic behavior of helium excited diatomic molecule (<i>a</i> 3Σ<i>u</i>+)

Takao, Satoshi; Kogoma, Masuhiro; Oka, T.; Imamura, Masashi; Arai, Shigeyoshi

doi:10.1063/1.439910

Cited by 31 publications

(3 citation statements)

References 42 publications

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“…In addition, several bands with moderate intensity are observed at 448, 465, 640, 656, and 925 nm. The emission at 656 nm could be attributed to the singly ionized helium atom, and the others correspond to the excited diatomic molecule, He 2 * (a 3 Σ

_{u}^{+}

) 8,9. These emission lines from helium species disappear in Figure 7(b) except for weak atomic bands at 588, 668, 766, and 728 nm.…”

Section: Resultsmentioning

confidence: 93%

Effects of Electrode Positioning on the Atmospheric‐Pressure DBD Plasma Torch

Kuwabara

Kuroda

Kubota

2005

Plasma Processes & Polymers

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Summary: Various positions of electrodes were examined for a double cylindrical barrier discharge plasma torch with a pulse‐modulated power source. It was found that a stable He plasma jet was generated when the inner electrode was earthed and withdrawn back into the outer electrode. The plasma jet could oxidize a polystyrene film surface and a greater effect was achieved when the film was treated in the plasma jet rather than in the afterglow region.

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_{u}^{+}

) 8,9. These emission lines from helium species disappear in Figure 7(b) except for weak atomic bands at 588, 668, 766, and 728 nm.…”

Section: Resultsmentioning

confidence: 93%

Effects of Electrode Positioning on the Atmospheric‐Pressure DBD Plasma Torch

Kuwabara

Kuroda

Kubota

2005

Plasma Processes & Polymers

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“…Following early studies of low pressure microwave gas discharges and applications in microelectronics, recent He work strongly focuses on high pressure plasmas (with or without selected impurities) for use in surface treatment, laser sources, plasma displays, and biology. With room temperature He * 2 densities up to 10 15 cm −3 [17,26,27,28], a compact 465 nm laser may be a useful high resolution dedicated probe for plasma diagnosis or study of rotational relaxation and collisional transfer rates [27,29], providing higher sensitivity and resolution than He or Xe excitation lamps [20,27] and tunable dye lasers [17,30]. The laser can also be used for new investigations in cold He gas where unusual spectral features, differences between isotopomers, and specific molecular dynamics are observed [10,31,32].…”

Section: Discussionmentioning

confidence: 99%

Using a cw 465 nm Laser to Probe Metastable He2 Molecules

2009

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A cw 465 nm laser has been built for sensitive detection of helium metastable molecules by resonant absorption on the a 3 Σ + u (v=0) − e 3 Πg(v=0) transition band. The frequency-mixing radiation is obtained from commercial laser diodes in a periodically-poled KTP non-linear crystal. The 1.3-nm tuning range includes the main rotational lines of 3 He2, 4 He2, and 3 He -4 He dimers. Measurements of absolute molecular densities down to a few 10 9 cm −3 are reported in low pressure (1−400 mbar) room temperature He gas excited by a weak rf discharge. Unsophisticated detection techniques provide signals with good signal-to-noise ratios thanks to the narrow absorption linewidths (a few GHz, due to Doppler and moderate collisional broadenings) in the fully resolved spectrum. Prospects for use or upgrade of this blue laser to probe the broadened and shifted molecular lines in condensed He are discussed. PACS numbers: 33.20.Kf, 42.65.Ky, He 2 metastable molecules, laser absorption, frequency mixing in PP-KTP, spectroscopy in dense He II. LASER SET-UP AND PERFORMANCESContinuous-wave frequency up-conversion is performed with a commercial 2×1×10 mm 3 crystal of periodically poled KTiOPO 4 (PP-KTP) (Raicol Crystals Ltd.), selected for optimal performance [13]. The crystal is phase-matched for frequency doubling at 930 nm. Given the prohibitive cost-to-power ratio of a custom made laser diode (LD) at 930 nm (more than twice higher price per item with only 40-mW output), emission at 465 nm is actually obtained by *

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“…in very-high-pressure discharges by Takao et al [43], but no further measurements have been made at lower temperatures.…”

Section: B Rovibrational Relaxation Of the Metastable He2 Moleculesmentioning

confidence: 97%

Reaction dynamics of metastable helium molecules and atoms near 4.2 K

1993

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Infrared absorption spectra from metastable helium atoms (2s S, 2s 'S) and molecules (a X"+) were previously acquired by irradiating dense helium gas near 4.2 K with a pulsed proton beam [R. L. Brooks, J. L. Hunt, and D. W. Tokaryk, J. Chem. Phys. 91, 7408 (1989)]. The molecular spectrum was unusual because the observed rovibrational distribution within the a X"+ state was far from thermal equilibrium.Three different rovibrational groups were observed: (i) v =0, N=1 ("thermal" molecules); (ii) u =0, 9 «N «21 (rotationally excited molecules); and (iii) 10«v «12, N=1 (vibrationally excited molecules).In this work, the time evolutions of members of these three molecular populations were studied both during irradiation and in the subsequent afterglow. In addition, the evolution of the 2s S -2p 'P atomic line was investigated. This study quantitatively explores the reaction dynamics of the metastable molecule in the gas phase near 4.2 K. Gas pressures between 100 and 750 Torr were used. Time-resolved data were taken with a transient-digitizer system and summed for several thousand cycles of the pulsed proton beam. The absorption measurements were converted to time-resolved number densities with the aid of theoretical transition moments. The analysis required that the data be fit to the solutions of sets of coupled differential equations with a nonlinear least-squares-fit routine. The results provide insight into the complicated reactions involved in generating the unusual molecular distribution and into the reactions between the metastable molecules, metastable atoms, and the background helium gas.PACS number(s): 34.50. Gb, 34.50.Lf, 82.20.Pm

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Optical absorption spectra and kinetic behavior of helium excited diatomic molecule (a 3Σu+)

Cited by 31 publications

References 42 publications

Effects of Electrode Positioning on the Atmospheric‐Pressure DBD Plasma Torch

Effects of Electrode Positioning on the Atmospheric‐Pressure DBD Plasma Torch

Using a cw 465 nm Laser to Probe Metastable He2 Molecules

Reaction dynamics of metastable helium molecules and atoms near 4.2 K

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