Electron-impact cross sections for deuterated hydrogen and deuterium molecules

Yoon, Jung‐Sik; Kim, Young Woo; Kwon, Deuk-Chul; Song, Mi‐Young; Chang, Won‐Seok; Kim, Chang-Geun; Kumar, Vijay; Lee, BongJu

doi:10.1088/0034-4885/73/11/116401

Cited by 43 publications

(38 citation statements)

References 148 publications

(277 reference statements)

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“…While we are able to see clearly the threshold for the polar dissociation continuum, both these measurements do not show such a threshold, strongly suggesting considerable contamination due to UV and metastable molecules. This contamination may also explain the observed deviation beyond 11 eV as both the UV and metastable molecule production start around this energy [19,25]. Recent CS calculations of the 14 eV DEA using a simple local complex potential model [18] and convolved with an energy spread of 300 meV were in agreement with the first measurements of Schulz [7] but are in disagreement with our results.…”

Section: Fig 1 (Color Online) Momentum Image Of Hsupporting

confidence: 50%

Dissociative Electron Attachment Cross Sections forH2andD2

et al. 2011

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New measurements of the absolute cross sections for dissociative electron attachment (DEA) in molecular hydrogen and deuterium are presented which resolve previous ambiguities and provide a test bed for theory. The experimental methodology is based upon a momentum imaging time-of-flight spectrometer that allowed us to eliminate any contributions due to electronically excited metastable neutrals and ultraviolet light while ensuring detection of all the ions. The isotope effect in the DEA process in the two molecules is found to be considerably larger than previously observed. More importantly, it is found to manifest in the polar dissociation process (also known as ion pair production) as well. DOI: 10.1103/PhysRevLett.106.243201 PACS numbers: 34.80.Ht Dissociative electron attachment (DEA) in hydrogen is of fundamental importance as one of the benchmark cases in atomic collisions. Together with its reverse process of associative detachment (AD), it is also relevant to the studies in astrophysics [1-3], development of ion sources [4], and in fusion edge plasmas [5,6]. Three distinct resonant processes leading to negative ion production (H À and/ or D À ) were studied and absolute cross sections (CSs)À , and its isotopologues HD and D 2 have been reported. These three processes are believed to proceed through the lowest attractive X 2 AE þ u state (4 eV process), the repulsive B 2 AE þ g state (7-13 eV process), and the attractive Rydberg excited state, 2AE þ g (14 eV process) leading to excited H (D). The peak cross section for the most abundant process at 14 eV in H 2 DEA was determined in two independent measurements to be 3:5 Â 10 À20 cm 2 [7] and 2:1 Â 10 À20 cm 2 [8]. These two CS values were the only ones available until now and therefore have been widely quoted and used in many applications. More recently, the CS for the 14 eV process was used to normalize the CS for the 4 eV process in relative CS studies [9,10]. It should be noted that the unusually small number of DEA CS measurements in hydrogen and the still high uncertainty in the CS is mainly due to its very low value. For example, the peak CS for H 2 DEA is 2 orders of magnitude smaller as compared to O 2 DEA. Another important characteristic of DEA in hydrogen is a strong decrease in the CS for heavier isotopologues, HD and D 2 [8,9], due to the strongly reduced survival probability of the dissociative channel.Additional data on DEA in hydrogen have been provided by other experiments: H À angular distributions [11], the strong dependence of DEA at 4 eV on rovibrational excitation [12], and the appearance of interference structures in the CS between 8-12 eV [11] and at 14 eV [13].Two more studies on the relative DEA cross section have been performed with emphasis on the vibrational excitation dependency of the 14 eV resonance in H 2 and D 2 [14] and on the electron energy resolution dependency of the experimental CS for the 4 eV process in H 2 [10]. Because of the increase of the DEA CS by orders of magnitude with vibrational excitation of the t...

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Section: Fig 1 (Color Online) Momentum Image Of Hsupporting

confidence: 50%

Dissociative Electron Attachment Cross Sections forH2andD2

et al. 2011

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“…We corrected the calculation using the electron-impact ionization cross sections adapted from the National Institute of Standards and Technology (Kim et al 2016) at 70 eV for hydrogen, methane, and carbon monoxide: σ H 2 = 1.021 Å 2 , σ CH 4 = 3.524 Å 2 , and σ CO = 2.516 Å 2 . The electron-impact ionization cross section of deuterium is similar to hydrogen, and so we used the same value (1.021 Å 2 ); see Rapp & Englander-Golden (1965), tables 77 and 161 in Celiberto et al (2001), and Yoon et al (2010). We used the same value for methane and fully deuterated methane as an approximation since σ CD 4 was not found in the literature.…”

Section: Resultsmentioning

confidence: 99%

Negligible photodesorption of methanol ice and active photon-induced desorption of its irradiation products

Cruz-Díaz

Martín-Doménech

Muñoz

et al. 2016

A&A

105

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Context. Methanol is a common component of interstellar and circumstellar ice mantles and is often used as an evolution indicator in star-forming regions. The observations of gas-phase methanol in the interiors of dense molecular clouds at temperatures as low as 10 K suggest that non-thermal ice desorption must be active. Ice photodesorption has been proposed to explain the abundances of gas-phase molecules toward the coldest regions. Aims. Laboratory experiments were performed to investigate the potential photodesorption of methanol toward the coldest regions. Methods. Solid methanol was deposited at 8 K and UV-irradiated at various temperatures starting from 8 K. The irradiation of the ice was monitored by means of infrared spectroscopy and the molecules in the gas phase were detected using quadrupole mass spectroscopy. Fully deuterated methanol was used for confirmation of the results. Results. The photodesorption of methanol to the gas phase was not observed in the mass spectra at different irradiation temperatures. We estimate an upper limit of 3 × 10 −5 molecules per incident photon. On the other hand, photon-induced desorption of the main photoproducts was clearly observed. Conclusions. The negligible photodesorption of methanol could be explained by the ability of UV-photons in the 114−180 nm (10.87−6.88 eV) range to dissociate this molecule efficiently. Therefore, the presence of gas-phase methanol in the absence of thermal desorption remains unexplained. On the other hand, we find CH 4 to desorb from irradiated methanol ice, which was not found to desorb in the pure CH 4 ice irradiation experiments.

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“…Finally, the QMS sensitivity is regularly calibrated by measuring the QMS signal as a function of a varying D 2 pressure, set in the oven chamber by an off-axis leak valve, which can be converted into a flux of D 2 entering the differential stage of the QMS thanks to the kinetic theory of gases. Since it is difficult to calibrate the QMS signal for HD products with the same method, we use instead the D 2 calibration corrected from their relative ionization cross sections [14,15] and the characterization of the mass dependent ion detection efficiency of our QMS [16].…”

Section: Temperature Programmed Desorption (Tpd) and Retention Calibrmentioning

confidence: 99%