Identification of intermediate radicals in theCH4microwave plasma by theLi+

Abstract

We (i) describe the complete Li -adduct mass spectrum of the CH4 microwave discharge plasma, obtained by ion attachment techniques, (ii) give evidence that many radicals are produced in the plasma, and (iii) present a preliminary spectral identification analysis. The identified species are C"Hz" (n =2-13), C"Hz"+l (n =2-13), C"H"(n =2,4, 5, 6), and so on. PACS number(s): 52.80.s, 35.20.WgIn order to demonstrate that a recent development of the Li+ ion attachment and quadrupole mass spectrometer technique for the sensitive detection of intermediate radicals will yield important data for various radical reactions, we have investigated the identi6cation of the principal radical species produced by the CH4 microwave (MW) discharge. We have succeeded in detecting various kinds of hydrocarbon polymer radicals, which were C"H2", (n =2-13), C"H2"+, (n =2-13), C"H"(n=2, 4, 5,6), and so on. The concurrent formation of these types of radials is experimental evidence on radical involvement in plasma-induced polymerization and may be characteristic of plasma, suggesting the importance of radical-molecule reactions in the plasma environment. Intermediate radicals have short lifetimes. Furthermore, their steady-state concentration in a reacting gas phase is sometimes low. The combination of small concentrations and short lifetimes has ofFered a real challenge to scientists [1].On the other hand, it has been widely recognized that neutral radical species are responsible for the plasma treatment [2-4], such as the deposition of hydrogenerated amorphous carbon thin films as well as crystal diamond films, the etching of highly integrated circuits, and surface graft polymerization.However, the difficulties of radical detection have hampered the development of insights into the process mechanisms.We believe that the present study concerns one of the most important problems that had to be resolved before the radical contribution to the total reaction schemes could be determined in plasma chemistry.The apparatus is shown in Fig. 1. A Shimadzu atmospheric pressure ionization quadrupole mass spectrometer with a Li+ ion attachment reaction chamber (RC) was used [5,6]. A stream of reaction products from a quartz discharge flow tube is directed into the alkali-metal ion attachment reaction chamber.The RC has a glass bead (Li+ emitter) which contains the alkali-metal oxide (lithium oxide in the present study) in an aluminosilicate matrix. By heating this bead, lithium ions are produced [7]. These parent ions, in turn, ionize the radical products (R ) by adduct formation (R+Li)+. (R+Li)+ complexes are formed by termolecular association reactions [8,9]. Parent-daughter ion cavity skimmer GH4 U 0 (R+Li) 0 0 lens glass lead (Li emitter) J I quadrupoles INW generator DP DP FIG.

Lithium ion attachment mass spectrometry: Instrumentation and features

“…[11][12][13][14][15][16][17][18][19][20] Highlights of the results from the above attempts are briefly summarized here.…”

“…With the aim of developing a more efficient and sensitive technique for detecting intermediate radical species in chemical reactions, Fujii has proposed 10 and developed [11][12][13][14][15][16][17][18][19][20] a novel method based on soft ionization Li ϩ ion attachment mass spectrometry (Li ϩ MS). The experimental details, operation, and unique features of a Li ϩ MS system are presented in this article.…”

Free radicals produced from thermally-irradiated polyethylene polymers: An ion attachment mass spectrometric study

“…The detection and evaluation of HC radicals in discharge plasma has been investigated by a variety of techniques [3][4][5][6][7]. Kojima et al [3] have reported the direct observation of methyl radicals using threshold ionization mass spectrometry.…”

“…Rudolph and Moore [5] measured mass spectra of free radicals from a microwave discharge in a fast flow of methane in argon and in hydrogen and reported the presence of many HC radicals, such as C 2 H 5 , C 3 H 3 , C 3 H 7 , C 4 H 5 , C 5 H 7 , C 5 H 9 , and C 5 H 11 . Fujii [6,7] examined methane microwave discharge plasmas using the Li + MS technique and detected longer-chain HC free radical species, such as C n H 2nÀ1 and C n H 2n+1 (n = 1-8), along with a few aromatic compounds.…”

Evolved gas analysis–ion attachment mass spectrometric observation of Mn(CO)5 and Mn2(CO)9 radicals produced by Mn2(CO)10 pyrolysis

“…ion-attachment mass spectrometric (IAMS) method [10][11][12][13][14]. IAMS is unique in that it provides only Li ?…”