Recombination of H3+ Ions in the Afterglow of a He-Ar-H2 Plasma

Recombination of H3+ with electrons was studied in a low temperature plasma in helium. The plasma recombination rate is driven by two body, H3+ + e, and three-body, H3+ + e + He, processes with the rate coefficients 7.5x10^{-8}cm3/s and 2.8x10^{-25}cm6/s correspondingly at 260K. The two-body rate coefficient is in excellent agreement with results from storage ring experiments and theoretical calculations. We suggest that the three-body recombination involves formation of highly excited Rydberg neutral H3 followed by an l- or m- changing collision with He. Plasma electron spectroscopy indicates the presence of H3.Comment: 4 figure

Temperature dependence of binary and ternary recombination of H3+ ions with electron

We study binary and the recently discovered process of ternary He-assisted recombination of H3+ ions with electrons in a low temperature afterglow plasma. The experiments are carried out over a broad range of pressures and temperatures of an afterglow plasma in a helium buffer gas. Binary and He-assisted ternary recombination are observed and the corresponding recombination rate coefficients are extracted for temperatures from 77 K to 330 K. We describe the observed ternary recombination as a two-step mechanism: First, a rotationally-excited long-lived neutral molecule H3* is formed in electron-H3+ collisions. Second, the H3* molecule collides with a helium atom that leads to the formation of a very long-lived Rydberg state with high orbital momentum. We present calculations of the lifetimes of H3* and of the ternary recombination rate coefficients for para and ortho-H3+. The calculations show a large difference between the ternary recombination rate coefficients of ortho- and para-H3+ at temperatures below 300 K. The measured binary and ternary rate coefficients are in reasonable agreement with the calculated values.Comment: 15 page

Comparative effect of interactive mobiles (clickers) and communicative approach on the learning outcomes of the educationally disadvantaged Nigerian pupils in ESL classrooms

Effective teaching that promotes learners’ active engagement and the development of communicative proficiency has been a challenge to teachers of English as a second language (ESL). Previous research on second language (L2) teaching has shown that L2 learners improve better in communicative skills when they are actively engaged, participate in communicative tasks that facilitate interaction and are provided with the opportunity to use the target language in the classroom. This study focuses on improving ESL learners’ learning outcomes in remotely-located primary schools in Nigeria. The study aimed to test whether the introduction of Personal Response System (PRS) and communicative approach can improve pupils’ English-language communicative competences and their attitudes towards English learning. Specifically, this study examined the extent to which significant differences exist in pupils’ communicative competence performance scores and learning gains based on teachers’ use of a communicative approach, PRS and lecture methods in the ESL classroom. Furthermore, the research also attempted to find out whether pupils’ attitudes towards the learning of English would significantly differ based on teaching strategy. Attitudes of pupils and teachers towards the interventions were also investigated. A pre-test and post-test non-randomised control group design was adopted in this study. Some qualitative data were also collected to augment the quantitative main data. Ninety nine pupils from three intact classes in different schools in Ijebu-North local government, Ogun-State, Nigeria were assigned to two experimental groups and one control group. In addition to the traditional use of textbooks, one of the experimental groups was taught using communicative activities, while the second experimental group experienced communicative tasks blended with the use of a personal response system. The control group received the conventional classroom instruction (lecture method), including the use of the English language textbook. In order to provide answers to the research questions and the hypothesis of this study, English Language Listening Tests and English Language Speaking Tests, Pupils’ Attitude to English Language Lesson Questionnaire, Pupils’ Attitude to Clickers’ Questionnaire and Pupils’ Attitude to Communicative Approach Questionnaire were administered at the pre-and post-test stages of the research. These instruments were also complemented with data from classroom observation, video recording of the instructional process, and audio-recorded interviews with the teachers and selected pupils in the experimental groups. The results indicate that the two experimental groups showed greater improvement in communicative competence than did the control group; but the PRS group improved more than the communicative approach group both in listening and speaking skills development. Moreover, pupils’ learning gains were statistically different, with the PRS group having the highest gain scores above the communicative approach group, while the control group did not experience increased learning gains. The results also reveal pupils’ mixed-reactions with respect to their attitudes toward the English language lesson and the interventions. Teachers’ attitudes toward the interventions were in the positive direction

Recombination Of H\u3csup\u3e+\u3c/sup\u3e3 Ions In The Afterglow Of A He-Ar-H2 Plasma

Recombination of H+3 with electrons is studied in a low-temperature plasma containing He, H2 and Ar at different He and H2 densities. The effective plasma recombination rate is driven by binary, H+3 + e-, and ternary, H +3 + e-+ He, processes with the rate coefficients 7.5 × 10-8 cm3 s-1 and 2.8 × 10-25 cm6 s-1 respectively at 260 K. We suggest that the ternary recombination involves formation of neutral highly excited Rydberg H3 followed by an l-changing collision with He. The difference between recombination of para- and ortho-H+3 is discussed. © 2008 IOP Publishing Ltd

Non-Maxwellian electron energy distribution function in He, He/Ar, He/Xe/H

Experimental studies of the electron energy distribution function “EEDF” under well defined conditions in flowing afterglow plasma, using a Langmuir probe are reported. The EEDF is measured in He2+ and Ar+ dominated plasmas and in XeH+ and XeD+ dominated recombining plasmas. He is used as a buffer gas at medium pressures in all experiments (1600 Pa, 250 K). The deviation of the measured EEDF from Maxwellian distribution is shown to depend on plasma composition and on the processes governing the plasma decay. The influence of energetic electrons produced during the plasma decay on the body and tail of the EEDF is observed. The mechanism of energy balance in afterglow plasma is discussed