Reactions of Laser Ablation-magnesium Plasma with Methanol Clusters Reactions of Laser Ablation-magnesium Plasma with Methanol Clusters

Reactions of Laser Ablation-magnesium Plasma with Methanol Clusters

  • 期刊名字:高等学校化学研究(英文版)
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  • 论文作者:ZHANG Shu-dong,KONG Xiang-he,Z
  • 作者单位:College of Physics and Engineering
  • 更新时间:2020-07-08
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论文简介

Available online at www.sciencedirect.com●CIENCE@oinect.CHEM. RES. CHINESE U.2006, 22(5), 621-625Reactions of Laser A blation-magnesium Plasmawith Methanol Clusters *ZHANG Shu-dong"" , KONG Xiang-he, ZHU Xiang-jun, WANG Yan and JIANG Su-rongCollege of Physics and Engineering, Qufu Normal University, Qufiu 273165, P. R. ChinaReceived Dec. 12, 2005The laser ablation-molecular beam( LA-MB) method is useful for studying the reactions of metal ions with molec-ular clusters. Reactions of magnesium plasma with methanol clusters were studied by using this method. A speciallydesigned reaction cell was used as a fast flow reactor operated under thermal conditions , and the reaction productswere measured with a tim-of-light( TOF) mass spectromneter. Surprisingly, several series of cluster ions with com-plex sizes and intensity distributios were obtained when the laser ablating was applied to dfferent parts of the molec~-ular beam. In the front part of the molecular beam, strong Mg* (CH,0H)。(n=0--5) and weak H* (CH,0H).(n=0- -5) cluster ions were observed with relatively small cluster sizes; in the middle part of the molecular beam,the main cluster ions were H* (CH,0H).(n=6-17) and H* (H2O)2(CH,OH)。(n=6- -17) with a relativelylarge cluster size and a weak intensity; in the back part of the molecular beam, two new series of cluster ions ,MgO* (H20)(CH,0H)。(n=6--10) and MgOCH; (CH,0H)。(n=6-10), were obtained and accompanied byweak H* (CH,0H)。(n=4- -7) and H* (H20)2 (CH,0H)。(n=3- 6). The formation mechanisms and speedcharacteristics of the cluster ions are discussed in this article.Keywords Laser ablation molecular beam; Mg plasm; Methanol cluster; Ion-molecular cluster reaction; Forma-tion mechanismArticle ID 1005-9040(2006)-05-621-05Introductiontransition metal ions with alcohols, ammonia or waterReactions of metal ions with neutral molecules ormolecular clusters'1- 6 . Fuke et al.印studied the pho-clusters produce a variety of metal complex ions andto-dissociation of Mg* (H20)。ions and reported be-other new series of cluster ions including cations andsides the evaporation of single neutral water molecules,anions. The laser ablation-molecular beam ( LA-MB )a photo-induced chemical reaction that resulted in themethod has marked its relevance in the studies on theformation of hydrated Mg* 0H ions. Lu and Yang21above-mentioned reactions. The interest in the reac-studied the reactions of alkaline-earth metal ions withtions of both ionic and neutral metal atoms with organicmethanol clusters and found two product switches: theclusters has increased dramatically in the past decade.first occurred at around n=5 from M* ( CH,OH)。toThe study of metal ion-solvent cluster reactions providesMOCH (CH,OH)m1, and the second occurred at ca.valuable information on their reactivity patterns ann= 15 from MOCH (CH20H)。1 to M*(CH,0H)transitions from a gas phase to a solution phase. Al-Selegue and Lsyl8.9] found a similar effect forthough numerous reports on the reactions of ions andM*(CH,OH)。(M = Na or Cs) clusters , which under-molecules are theoretically and experimentally availa-go an intracluster reaction in the ground electronic stateble, the studies on the reactions of molecular clustersto eliminate diethyl and forn M* (CH,OH)-2(H20).with laser ablation-metal plasmas are few.The“ mixed solvent ”product cluster intensities in-Clusters combined via van der Waals forces orcrease as a function of the cluster size but do not sur-hydrogen bonding are the ideal medium for studyingpass those of the parent M* ( CHgOH)。, suggestingthe reactions of metal ions with molecular clusters.that a full “product switch" does not occur.Most studies have been carried out for the reactions between alkali metal ions, alkaline-earth metal ions, orplesmn中国煤化工small reaction cel:YHCNMHG* Supported by the Doctoral Startup Foundation from Qufu Normnal Unuversity.* *To whom correapondence should be addressed. E mail: zhangsd2@ 126. com622CHEM. rES. CHINESE U.Vol. 22by using the LA-MB method. Abundant cluster ionsResultswere found ,whose distributions in intensity and sizeTo determine the metal ions that participate in thechange along with laser ablation in diferent parts of theion-molecular cluster reactions, the TOF mass spectramolecular beam.of magnesium ions were measured when only an Mg tar-Experimentalget was ablated by laser, and the pulse valve wasA schematic view of the apparatus is shown inclosed. By changing the delay time from the beginningFig. 1.of the ablating of laser to the high voltage emerged onGa inletthe TOF electrodes ( referred to as “HV delay time'Pulse valvehereinafter for convenience) , the Mg ions produced byPulse vaIve- -00一laser ablation plasmas with diferent flying time lengthsMetal tasget吧NHd.YAG loto the TOF detecting area were measured, as shown inFig. 2.sSiP[6吨HVpulemo1o:Glass winriow0.16「(A) 合入Skimner1MS.; 0.12 tTime soquenceIDnreor0.08 t马HVpulse 1000VE 0.04 t1200 VFig. 1 Schematic diagram of the experimental0.00setup.456。4A small reaction cell made of Telon as a circularm/zcylinder with an inner diameter of 10 mm and a length0.12[ (B-144逞of 22 mm was fixed at the exit of the pulsed valve( Gen-; 0.08-104eral 9, with a nozzle of0. 8 mm in diameter). The fo-cused pulse laser( LAB-170, 532 nm, 10 ns, SpectraPhysics) , passed through the glass window of the reac--24tion cell and ablated on the surface of magnesium target(purity greater than 99. 9%). The target, which wasplaced 10 mm downstream from the pulsed valve, was13060driven by a step motor. The gas mixture of methanol-Fig.2 Mg ions mass spectra.helium was formed by bubbling the helium gas through(A) A tpieal mass spectrum; (B) mass spectraa methanol liquid reservoir. The methanol clusters wereat diferent HV delay time.produced by supersonic expansion of the methanol-heli-Single- and double-ionized Mg ions were ob-um gas mixture through the pulsed valve nozzle.served ,and they lasted for a period of time with respectAs the molecular beam passed the reaction cell,to the HV delay time from 14 to 150 μs and from 14 tothe Mg target was ablated by the Nd: YAG laser and Mga. 30 μs, respectively. Meanwhile, the Mg isotopeplasma was produced, and the reactions between the ions were also observed, and their intensities wereMg plasma and the methanol clusters took place. Thecoincident with the abundance ratio ( 2Mg,79% ,products passed through the skimmer and entered a "Mg, 10%,2Mg, 11%).Time-of-light( T0F) mass spectrometer where the clus-The reaction products of the Mg plasma reactingter ions were extracted by applying pulsed high voltages with methanol clusters were abundant and complex.of 1200 and 1000 V with 6 μs widh to the electrodeSeveral series of cluster ions were observed when theplates, respectively. The ions were accelerated andlaser delay time to the opening of the pulse valve was inmoved to the field-free drift tube and then reached thethe range of 200- -1400 μs. The mass spectra are dif-micro-channel plate ( MCP) detector. The time se- ferent at diferent laser delay time, but at the same la-quence of the opening of the pulse valve, laser firing,ser del中国煤化工imilar except forand pplication of pulsed high volage was contrlled by obviouYHferent HV delaya 5-channel pulse generator( CH032 , University of Sci-timeCNMHGmassectaatence and Technology of China) .different laser delay time.ZHANG Shu-dong et al.6230.04 Pm=123456(A)加579111315(B)0.12李(C)Mg+ (CHgOH)。0.05- Mg+ (CH2OH).0.030.040.08 t0.02 tH+ (CHzOH)。0.0201421314560.01H+ (CH)0H)。=.5678日0.00 M人~0.001020030040050060050100 150 200 25060 120 180 240(D|皇(E0.000. 006g"o.000MgO+ (H2O)(CHzOH)。270 300 330 360=78910n=6. 912150.004H+(H2O)(CH2OH.。n=789≈=8 1p12 H+(H2O)2(CH;OH).MgOCHt (CH;OH)。置0.002 |H+ (CH,OH)。0. 002 t.n=4567H+(CH2OFD.0. 000 I0. 000 t150300 450 60080 160 240 320 40m/zm/xFig.3 TOF mass spectra produced by a laser ablation magnesium plasma reacting with methanol dlusters.The laser delay time to the opening of the pulse valve: (A) 200 s; (B) 300 μ; (C) 400 μ; (D) 800 μ; (E) 1200 u.When the laser delay time was about 200 μ8 ,at the back part of the molecular beam is consideredcorresponding to the laser ablating at the front part of[Fig. 3(D),the inset is a part of the magnifiedthe molecular beam, Mg* ( CH,0H)。(n=0- -5) clus-scheme ].ter ions were observed with intensities decreasingWhen the laser delay time was about 1200 μs,monotonically and the cluster size increasing. Mean-two new series of cluster ions appeared namelywhile, H* (CHgOH)。cluster ions with similar sizMgO *(H20)(CH20H)。(n=6- -10) and MgOCH;'●appeared with a relatively weak intensity, as shown in( CH,OH)。(n=6- -10). Meanwhile , relatively smal-Fig. 3(A).ler size: H* (H20)2 (CH,0H)。(n =3-6) andWhen the laser delay time increased to aboutH'(CH,OH)。(n=4-7) were observed with rela-300 μs,the relatively larger size cluster ions oftively weak intensities [ Fig.3(E)].Mg* (CH,OH)。(n=6--17) were obtained, and theThe distance between the laser ablating region andintensity distribution expanded around at n=11 as itsthe TOF detecting area was 16 cm. By measuring thepeak value. The H* ( CH,OH)。cluster ions had weakT0F of the cluster ions from the laser ablating area tointensities and seemed to be submerged by thethe TOF area, the speed of the cluster ions can beMg* (CH,0H)。cluster ions , which displayed a broad-easily estimated.ened peak base, as shown in Fig. 3(B).Fig. 4 shows the speed distribution of the totalWhen the laser delay time was in the range ofcluster ions at different laser delay time. It is clear that400- -700 μs,corresponding to the laser ablating atthe cluster ions were produced when laser ablating atthe middle part of the molecular beam, only strongthe front and back parts of the molecular beam had aMg* and weak Mg* ( CH,OH) peaks were observed.1800卜Compared with the above results, the intensity of theions considerably increases as shown in the longitudinalcoordinate scale changes in Fig. 3(C).目1400When the laser delay time was about 800 μs,besides Mg* ( CH,0H)。(n =0- -2) ions, mixed1200protonatedwater-methanolH* (H20)2(CH,0H)。(n = 6-17),accompanied中国煤化工with protonated methanol cluster ions, H* ( CH,OH)。MYHCNMHGoo 1200 1400(n=6-17), were observed with relatively weak in-Laser delay time/ustensities. This time corresponding to the laser ablatingFig.4 The speed distribution of the molecular beam.624CHEM. RES. CHINESE U.Vol. 22relatively low speed. Comparing the product distribu-(CH,0H)n, and( CH,COCH3). in a gas phase- 61 .tion with different laser delay time as shown in Fig. 3,The formation mechanisms are assumed to be direct as-it can be seen that Mg* ( CH,OH)。ions accompaniedsociation of metal ions with molecular clusters accom-with weak H*(CH,OH)。 ions were mainly formedpanied by some neutral molecules vaporizing to leasewhen the molecular beam speed increased( laser delayextra inner energy or rearrangement occurring after thetime in the range of 200- -400 μs); when the beamassociation and vaporization. It is still possible thatwas at its highest speed, only strong Mg* and weakcertain H elimination or H2 elimination reactions occurMg* (CH3OH) ions were formed ( laser delay time inafter the association of metal ions with molecular clus-the range of 400- -800 μs); large-sized cluster ions ofIn the proposed experiment, the metal complexH'( H20)2( CH,0H)。and H* (CH,OH)。were pro-cluster ions Mg* ( CH,OH)。were observed, and it isduced when the beam speed decreased ( laser delayassumed that their formation may have a similar mecha-time in the range of 800-1200 μs ); thenism as mentioned above. The process may be ex-Mg0* (H20)(CH,0H)。and MgOCH; ( CH,0H)。pressed as a direct association and subsequent intra-cluster ions were formned only at the back part of thecluster rearrangement.beam with a low speed( laser delay time in the range ofMg*" + (CH,0H)。-→+Mg* (CH,0H):→1200--1400 μs).(rearrangement) - +Mg*(CH,0H)m + (CHgOH)。_mDiscussionThe formation mechanism of protonated clusterAccording to the supersonic expansion theory ofions H* ( CH,OH)。has been discussed in literature,molecular beams, when a molecular beam is jetted outbut the conclusions are not unanimous. Shilnl usedfrom a pulsed valve, methanol clusters may be pro-vacuum ultraviolet light(118 nm) to ionize( CH,0H)。duced from methanol molecules combined with hydro-and( C2H,OH)n, and protonated cluster ions, such asgen bonds. Each pulse molecular beam must last someH*(ROH),(R=CH3, C2Hs,n=1- -5), were meas-time, and it can be assumed that the front and theured. The H * ( ROH)。cluster ions were consideredback parts of the molecular beam have lower pressureso have resulted from the dissociation of the neutraland densities, and the middle part of the molecularparent ( ROH). Morgan(12) used 266 nm laser tobeam has a higher pressure and density.ionize ( CH,OH)。clusters, and H* ( CHzOH). anWhen the beam passes the reaction cell, its pre8-H'(H20)(CH,OH)(m >7) were observed. There-sure change will affect the laser ablation condition. Orlando' 10 used the molecular dynamics method to simu-fore , the formation of H* (CH,OH)。was considered tolate the reaction of Cs * with methanol clusters and con-be the result of the fast-proton transition reaction aftercluded that the cluster ions' distribution, translationalthe ionization of( CH,OH)。,that is,(CH,OH):→H*(CH,0H)21 +CH,0energy,, vibrational and rotational states are relatedwith collision energies.Lu[2] also observed weak H* (CH,OH)。(n<9)The results indicate that when the collision energyions in the reaction between Mg°' and( CH,OH)。with-is less than 8 eV( called viscous collision) , large-clus-out using a reaction cell similar to that in this study andters may be formed; when the collision energy is grea-considered that H* ( CHzOH)。would be produced byter than 12 eV( called elastic collision),small clustersthe electron impacting ionization of( CH,OH)。. Com-are easily formned because a higher collision energy mayparing these results with the proposed experimentcause neutral clusters to dissociate.results,it was considered that the formation oWhen the laser ablating is at the front part of theH*(CH,0H)。is also related with the electrons of themolecular beam, corresponding to the laser delay timeMg plasma. Electrons collide with ( CH,OH )。clustersin the range of 200- -300 μs and the molecular beamand result in the ionization of the ltter, and then a fasthas a relatively low density, the Mg plasma producedproton transition reaction occurs inside the cluster ions,by laser ablation may still have a higher kinetic ener-and H*(CH,OH)。is formed at last, that is,gy,90 the collision energy between Mg * and methanole+ (CH20H),→(CH2OH): +2e-→clusters is still high, leading to a relatively strong reac-H* (CH,0H)1+ CH20 +2etion and only cluster ions of small sizes are formned.When the laser delav time is in the range of 400-Metal-complex cluster ions have been observed in 700中国煤化工ablaing at the mid-the study of alkali metals, alkaline-earth metals, ran- dleYHCNMHGbeamhasthehigh-sition metals reacting with (H20),(NH), et densly ana mngnest speed, and the clisin energy .No. 5ZHANG Shu-dong et al.625may be high enough that neither large cluster ions canters in gas phase was studied by using the method ofhe forned nor can they be decomposed to monomers.LA-MB.Some positivecluster ions, such asinerefore, only Mg* and Mg* ( CH,OH) will be ob-Mg*(CH,0H)。(n=0- 5), H' (CH3OH)。(n=0-served.5),H' ( H20)2 ( CH,OH)。(n = 6-17),When the laser ablating takes place at the backMgO*(H20)( CH,0H),(n=6--10) and MgOCH;●part of the molecular beam, corresponding to the laser(CH,0H)。(n=6-10), were observed. The cluster-delay time in the range of 800- -1200 μ8, the speed ofion distributions, cluster species, intensties and sizethe molecular beam decreases. It is assumed that therechanges, have a strong relationship with laser ablatingis a higher probability for; reactants to collide withdelay time. The formation mechanisms and speed char-each other, and intracluster reactions may occur.acteristics of the cluster ions have been discussed.Koo et al. (6] studied the ion-molecular reactions ofTi * with methanol clusters using the similar method asAcknowledgmentsproposed in this study. They also observed several se-The authors thank Professor Xia Yun-jie and Pro-ries of cluster ions such as Ti* (OCH,) ( CH,0H)。,fessor Wu Fu-quan for their assistance in the experimentsTi+(OCH,)2(CH,0H)。,Ti0* ( CH,0H)。,andand discussions.Ti0H* (CHgOH)。The Ti* (0CH,) ( CH,0H)。andTi* ( OCH, )2( CH,OH)。were atributed to the hydro-Referencesgen elimination reactions(- -2H or-H2) of the Ti*[1] Kaya T., Horiki Y.,Kobayahi M., e al, Chem. Phys.Le. , 1992, 200, 435ions within the heteroclusters. The TiO* ( CH,OH)。[2] LuW. Y., YangS. H,1 Phys. Chem. A, 1998, 102, 825and TIOH* ( CH,OH)。were interpreted to arise from[ 3] Saneksta M., Misaizu F., Fuke K., a al. J. Am. Chen.the insertion of Ti* ions into the C- -0 bonds inSoc, 1995, 117, 747CH,OH, followed by CH, and CH, elimination from[4] LiC. s., CaoZ. x., Wu W.. et al, Chem. 1. ChineseUniersitie, 2005, 26(1), 116the [ CH,- -Ti*- -OH ] internediate, respectively.[5] WangY. J, CaoZ. x, ZhangQ. E, Chem. J. ChineseThe formation of MgO* ( H20) ( CH,OH)。 andUniersie, 2003, 24(4), 678MgOCH;' (CH20H)。in this experiment may fllwl the[6] KooY. M., KimJ. H., ChoiY. K.,eal,J. Phys. Chem.A, 2002, 106, 2465same route, in which the insertion reaction of Mg* into[7] Misaizu F., Sanekata M., Fuke K, J. Chem. Phy. , 1994,C-0 or 0--H bond and 2H一or H2 - - elimination100, 1161reaction occurs in Mg* ( CH,OH).. The process can[8] SelegpueT. J, LiayJ. M,I. Am Chem Soc, 1994, 116,4874be summarized as follows:[9] DravesJ. A., LisyJ. M.,J. Am Chem. Sc., 1990, 112,Mg* (CH,0H)m- +MgOCH; (CH,OH)。+9006H2 +(m -n)( CH,OH) .[10] Orlando M. C., Liay J. M,Int. J. Mass. Spee, 1999,Mg* (CH,0H)m-→Mg0*( CH,OH)m-1 + CH,185/186/187, 883Mg0* (CH,0H)。-→Mg0* (H20)(CH,OH)m-2 +[11] ShiY. J, ConstaS., Das A. K, J. Chem. Phys. , 202,116, 699(CH,0CH,)[12] MorganS., KeeeR. C., CastlemanA. w.,1 Am. Chem.ConclusionsSo. , 1989, 11, 3841The reaction of Mg plasma and (CH,0H)。clus-中国煤化工MYHCNMHG

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