High Resolution Crossed Molecular Beams Study on the F+HD HF+D Reaction at Collision Energy of kj/mol

Transcription

1 CHINESE JOURNAL OF CHEMICAL PHYSICS VOLUME 24, NUMBER 5 OCTOBER 27, 211 ARTICLE High Reslutin Crssed Mleular Beams Study n the F+HD HF+D Reatin at Cllisin Energy f kj/ml Wen-rui Dng, Chun-lei Xia, Ta Wang, Dng-xu Dai, Xiu-yan Wang, Xue-ming Yang State Key Labratry f Mleular Reatin Dynamis, Dalian Institute f Chemial Physis, Chinese Aademy f Sienes, Dalian 11623, China (Dated: Reeived n July 8, 211; Aepted n July 25, 211) The dynamis f F+HD HF+D reatin has been studied at ten llisin energies ranging frm 5.43 kj/ml t kj/ml using high-reslutin H/D atm Rydberg tagging time-f-flight methd. Prdut vibratinal and rtatinal state-reslved differential rss setins have been determined. The intensity f the HF(v =2) frward prduts dereases as the llisin energy inreases, suggesting that the resnane ntributin is redued as the llisin energy inreases. The frward peak f HF(v =3) prdut has als been bserved abve the threshld f this prdut hannel. Prdut energy dispsals in different degrees f freedm have been analyzed. The llisin energy dependene f the HF vibratinal prdut branhing was als determined. This wrk presents a mprehensive dynami piture f this resnane mediated reatin in a wide llisin energy regime, prviding a gd test grund fr theretial understandings f this interesting reatin at higher llisin energies. Key wrds: F+HD HF+D, Crssed mleular beam, Rydberg tagging, Reative resnane I. INTRODUCTION The F+H 2 reatin and its istpi variants have been extensively studied by experimental and theretial sientists beause f its imprtane in the develpment f reatin dynamis. Sine the first theretial preditins f dynamial resnane in the F+H 2 reatin [1 3], searhing fr experimental evidene f reatin resnane has beme a entral issue in the study f hemial reatin dyanmis. Neumark et al. perfrmed a landmark rssed-beams experiment n the F+H 2 reatin using the universal rssed mleular beams tehnique [4, 5]. A lear frward sattering peak was bserved fr the HF(v =3) prdut, whih was attributed t reatin resnanes in this reatin. Furthermre, frward sattering fr the DF(v =4) prdut frm F+D 2 as well as the HF(v =3) prdut frm F+HD was bserved [6], nsistent with the F+H 2 experiment [4]. Exat quantum mehanial (QM) sattering alulatins f the F+H 2 reatin [7] n the Stark-Werner PES (SW-PES) [8] shw that HF(v =3) frward sattering did nt have a lear signature f a reatin resnane. Quasi-lassial trajetry (QCT) alulatins n the SW surfae by Aiz et al. als exhibit frwarding Part f the speial issue fr the Chinese Chemial Siety s 12th Natinal Chemial Dynamis Sympsium. Authr t whm rrespndene shuld be addressed. xmyang@dip.a.n sattering f HF(v =3) in the same reatin [9], implying that HF(v=3) frward sattering is prbably nt related t a quantum resnane. Clearly, the SW-PES is reasnably aurate in desribing the transitin state regin fr the F+H 2 reatin as revealed in the negative in phtdetahment study f the FH 2 system [1 12]. Therefre, the assignment f the HF(v =3) frward sattering t the reatin resnane is ertainly questinable. Liu and wrkers arried ut a rssed beam experiment n the F+HD HF+D reatin, and bserved a step r a peak in the exitatin funtin at the lw llisin energy [13, 14], whih was attributed t reatin resnane in the F+HD reatin. In additin, Liu and wrkers measured differential rss setins fr the same reatin in a wide llisin energy range frm 1.67 kj/ml t kj/ml [15, 16], and nluded that at llisin energy lwer than 5.2 kj/ml, the reatin preeds almst exlusively thrugh resnane tunnelling. In the ase f the F+H 2 reatin, n peak in the exitatin funtin has been bserved by Liu and wrkers. In a series f mbined experimental and theretial studies f the F+H 2 reatin with full prdut quantum state reslutin in ur labratry, we have bserved lear Fehbah resnanes [17 22]. A new and imprved ptential energy surfae, XXZ-PES was nstruted t eluidate the resnane in the reative system [23]. Fr the F+HD HF+D, we have als perfrmed a series f high reslutin rssed mleular beam experiments [24] in the llisin energy range f.84 kj/ml DOI:1.188/ /24/5/ Chinese Physial Siety

2 58 Chin. J. Chem. Phys., Vl. 24, N. 5 Wen-rui Dng et al. t 5.2 kj/ml. The istpe effet n Fehbah resnanes in this system has been larified by a highly aurate CCSD(T) ptential energy surfae, XZ-PES. A lear physial piture f reatin resnanes in this benhmark system has been well estalished, whih is imprtant in the llisin energy regin (<6.27 kj/ml). The dynamis f this benhmark system in the higher llisin energy regin, hwever, has reeived less attentin. As mentined abve, Liu and wrkers [15, 16] has perfrmed a detailed rssed study n the F+HD reatin in the higher llisin energy range, in additin t the riginal wrk by Lee and wrkers [6]. Hwever, bth experiments were arried ut at relatively lwer reslutins. Therefre, it is neessary t reinvestigate the dynamis f the F+HD HF+D reatin at higher llisin energies. In this wrk, we have arried ut a high reslutin rssed beam experiment n the F+HD HF+D reatin at llisin energies frm 5.43 kj/ml t kj/ml, using the high reslutin H-atm Rydberg tagging tehnique. II. EXPERIMENTS Full quantum state reslutin rssed mleular beam sattering experiment n the F+H 2 and its istpi variants has been arried ut in ur labratry using the D-atm Rydberg tagging time-f-flight (TOF) tehnique. The experiment was nduted in a rssed beam apparatus, whih has been desribed in details previusly [25]. The duble skimmed F atm beam was prdued by the duble-stage pulse disharge f F 2 (5% in He at 4 kpa). The F atm in the beam was fund t be mainly in the grund state F( 2 P 3/2 ) and nly a small amunt f the spin-rbit exited F ( 2 P 1/2 ). The rati between F and F was abut 1.7, whih was determined thrugh vauum ultravilet (VUV) synhrtrn inizatin. In rder t have a better reslutin f the experiment, the HD beam was btained by expansin f the neat HD sample thrugh the liquid-nitrgen led general pulse valve. At llisin energy f 11.2 kj/ml and abve, in rder t reah the higher llisin energy and als t detet the full angle f the prdut in the enter-f-mass (CM) frame, the HD beam was expansed thrugh the Even-Lavie supersni pulse valve in rm temperature. The rtatinal distributin f the HD beam is almst all in j = fr the frmer and abut 88% in j =, 9% in j =1, and 3% in j =2 fr the latter methd. The rati f the rtatinal distributin was measured using the resnane enhaned multiplephtn inizatin (REMPI) methd. The D-atm prdut was first exited frm the grund state (with priniple quantum number n=1) t n=2 by the nm VUV light whih is generated by a tw-phtn resnane (2ω 1 ω 2 ) fur-wave mixing sheme in a Kr/Ar gas ell. Then the D-atm f n=2 was sequentially exited t the high Rydberg state with n 5 by the 365 nm light. The lng-lived Rydberg D-atms fly abut 317 mm befre they were field-inized by the eletri field applied in frnt f the mirhannel plate (MCP) detetr whih vers the detetable angle frm 45 t 135, s we an bserve the prdut in full angle frm frward t bakward in the CM frame. The signal deteted by the MCP detetr is subsequently amplified by a fast preamplifier, and then unted by a multihannel saler (MCS). One f the mleular beams was rtatinable, s we an hange the llisin energy nveniently by simply altering the rssing angle f the tw beams. In this way, we perfrmed experiment at ten llisin energies frm 5.43 kj/ml t kj/ml. III. RESULTS A. HF prdut velity distributins In this experiment, the TOF spetra f the D atm prdut at 18 different angles frm the F+HD reatin have been measured at ten different llisin energies. These TOF spetra were then nverted int prdut velity distributins. Figure 1 shws the D prdut velity distributins at three different sattering angles f frward, bakward and sideway, at fur typial llisin energies. In the first rw f Fig.1, three velity distributins at the llisin energy f 5.43 kj/ml were shwn. Clearly, HF(v =2) prdut is the dminant prdut in all sattering angles at this llisin energy. In the frward and the bakward diretin, the HF(v =2) prdut peaks at j =2; while in the sideway diretin it is rtatinally muh htter with a peaked distributin at abut j =1. HF(v =1) prdut is als present at this llisin energy. In the bakward diretin, the HF(v =1) prdut seems t have a bimdal struture in rtatinal distributin whih peaks at abut j =4 and j =11. At the llisin energy f 8.69 kj/ml, the verall features f the HF(v =1) and HF(v =2) prduts are quite similar t that f 5.43 kj/ml. Hwever, in the frward and bakward diretins, the HF(v =1) and HF(v =2) prduts are mre rtatinally exited. At this llisin energy, the HF(v =3) prdut appears beause the llisin energy is already abve the threshld f this prdut hannel. In the HF(v =2) frward diretin, in Fig.1(f), n HF(v =3) prdut was deteted beause f the sattering kinematis at the sattering angle. We have sanned many sattering angles, s the full DCS fr the HF(v =3) prdut an still be btained. At the llisin energy f kj/ml, the rtatinal distributin f the HF(v =2) bemes even htter as the sattering angle hanges frm bakward t frward diretin. The rtatinal distributin peaks arund j =5 in the bakward diretin, while it reahes its maximum distributin at j =13 in the frward diretin. Fr the HF(v =1) prdut, the rtatinal distributin peaks arund j =11 in the bakward diretin and bemes a DOI:1.188/ /24/5/ Chinese Physial Siety

3 Chin. J. Chem. Phys., Vl. 24, N. 5 Crssed Mleular Beams Study n the F+HD HF+D 59 FIG. 1 Velity spetra f the D-atm prdut frm the F+HD reatin in the bakward (left panel), sideway (medium panel), and frward (right panel) diretin at fur llisin energies inditaed. Nte: the labratry angles labelled at the tw higher llisin energies are different frm the tw lwer llisin energies beause the tw beam sures were swithed fr high llisin energy experiments. (a) () 5.43 kj/ml, (d) (f) 8.69 kj/ml, (g) (i) kj/ml, and (j) (l) 16.8 kj/ml. little ler when shift t sideway. It is neesary t pint ut that the reslutin is better fr the prdut velity distributins at llisin energies in the range f kj/ml frm whih at the llisin energies in the range f kj/ml. In the range f kj/ml, the data were measured using a liquid nitrgen led HD beam, while in the higher energy regin, the experiment was arried ut with a rm temperature HD beam. DOI:1.188/ /24/5/ Chinese Physial Siety

4 51 Chin. J. Chem. Phys., Vl. 24, N. 5 Wen-rui Dng et al. HD F (a) HF(υ'=3) HF(υ'=2) (b) () HF(υ'=1) HF(υ'=) (d) (e) (f) (g) (h) (i) (j) FIG. 2 The experimental 3D ntur plts fr the prdut translatinal energy and angular distributins fr the F+HD reatin at varius llisin energies: 5.43 kj/ml (a), 6.69 kj/ml (b), 7.77 kj/ml (), 8.69 kj/ml (d), 9.95 kj/ml (e), 11.2 kj/ml (f), 12.7 kj/ml (g), 14.5 kj/ml (h), 16.8 kj/ml (i), kj/ml (j). B. Prdut differential rss setins Frm the fitting velity distributins, as shwn in Fig.1, rvibratinal state distributins f the HF prdut an be btained at different CM sattering angles fr any speifi llisin energies. Frm these quantum state speifi differential rss setins, we an then nstrut a three dimensinal (3D) DCS ntur fr the F+HD HF+D reatin at eah llisin energy studied in this wrk. Figure 2 shws the 3D DCS ntur at 1 llisin energies ranging frm 5.43 kj/ml t kj/ml. In the 3D DCS nturs, eah ring rrespnds t a speifi rvibratinal state f HF. Prminent lustered strutures an be assigned, frm the innermst ne, t HF (v =3, 2, 1, ). Figure 2(a) shws the 3D DCS nturs at the llisin energy f 5.43 kj/ml, n HF(v =3) prdut is bserved beause the llisin energy is belw the the threshld f this hannel, whih is alulated t be abut 5.6 kj/ml, slightly different frm the earlier value f 4.85 kj/ml estimated by Liu and wrkers [15, 16]. In their analyses, the exthermiity f the title reatin is kj/ml, and the frmatin f the HF(v =3) needs kj/ml [15] while in ur simulatin the tw energies are and kj/ml, repetively. At all the llisin energies that abve the threshld f HF(v =3), the frward peaks f this hannel are signifiant. As the llisin energy inreased, the bakward prdut f HF(v =2) shifts twards sideway while the frward prdut dereases after it reahes maximum f 6.69 kj/ml. At the five lwer llisin energies, the HF(v =1) prdut have small distributin in the frward diretin althugh the prdut flux f this hannel is dminated in the bakward. The branh rati f the HF(v =1) prdut rise with llisin energy and bemes the mst ppulated state at llisin energies higher than 14.8 kj/ml. Sine its nset at 7.65 kj/ml, the HF(v =) prdut branhing als inreases as the llisin energy ges up. Extensive study n this reatin has been dne by Liu and wrkers [15, 16]. In their previus experiment, they have als measured prdut 3D DCS at many llisin energies. We have made sme mparisns between their results and ur results, it seems there are sme ntieable diffrenes. The mst bvius differene is arund 8.36 kj/ml. Liu s results shw a prminent frward peak f HF(v =2) while nly a little prdut flux in the bakward diretin, while ur experiment indiates that mst f the HF(v =2) prdut appears at the bakward diretin and nly a narraw peak is present at the frward diretin at 8.69 kj/ml. This is prbably hard t attribute t the small differene in the llisin energy (.33 kj/ml). These differenes uld be aused by the different experimental DOI:1.188/ /24/5/ Chinese Physial Siety

5 Chin. J. Chem. Phys., Vl. 24, N. 5 Crssed Mleular Beams Study n the F+HD HF+D 511 FIG. 3 Ttal and vibratinal state-reslved CM DCS at ten llisin energies: 5.43 kj/ml (a), 6.69 kj/ml (b), 7.77 kj/ml (), 8.69 kj/ml (d), 9.95 kj/ml (e), 11.2 kj/ml (f), 12.7 kj/ml (g), 14.5 kj/ml (h), 16.8 kj/ml (i), and kj/ml (j). v =, v =1, v =2, v =3, and ttal. nditins. In ur experiment, the HD meluels in the beam are nearly all distributed in the j = state, while in Liu s experiment, there is a signifiant amunt f the j =1 state [15, 16]. The mleular beam nditins are als slight different in the tw set f experiment. The 3D DCS nturs in Fig.2 prvide a rather mplete view f the reatin dyanmis hange in the F+HD HF+D reatin as the llisin energy varies frm 5.43 kj/ml t kj/ml. By integrating the rtatinal ppulatins fr eah vibratinal state f the HF prdut at speifi sattering angles, we an determine the angular distributin f the HF prdut n v =, 1, 2, 3 vibratinal states. Figure 3 shws the angular distributins f vibratinal state speifi HF prduts frm F+HD HF+D at the ten llisin energies studied in this experiment. Frm these results, it is interesting t ntie that the angular distributins fr different HF vibratinal state prdut are very different. In the frward diretin, the ttal sattering flux f the title reatin are mainly frm the HF(v =2) and HF(v =3) prduts thrughut the llisin energy regin we have studied. The ntributin f the HF(v =2) and HF(v =3) is mparable in the frward diretin, whih seems t be in nflit with the 3D DCS in Fig.2. This phenmenn is due t the fat that the rtatinal distributin f the HF(v =3) is muh narrwer than HF(v =2) in the frward diretin. As the llisin energy inreased, the HF(v =2) have mre sideway ntributin while the HF(v =1) have mre bakward sattred ntributin. By integrating the angular distributins fr speifi vibratinal state HF prdut at different llisin energies, the dependene f the relative vibratinal state branhings f the HF prdut was determined and is FIG. 4 Prdut vibratinal branh rati hange with llisin energy. shwn in Fig.4. Interestingly, the realtive branhing f HF(v =) and HF(v =1) prduts inreases as the llisin energy inreases, while that f HF(v =2) and HF(v =3) dereases as the llisin energy inreases. The dynamial rigin f these variatins is, hwever, nt immediately lear. C. Prdut energy dispsals By fitting the TOF spetra f the D atm prdut, we have batined detailed rtatinal and vibratinal state distributins f the HF prdut at different llisin energies. Using these infrmatin, the prdut energy partitin in translatin, vibratin, and rtatin in this reatin an be determined. Figure 5 shws the angluar dependene f the energy dispsal in the rtatinal f r, vibratinal f v, and translatinal f t energy. The r- DOI:1.188/ /24/5/ Chinese Physial Siety

6 512 Chin. J. Chem. Phys., Vl. 24, N. 5 Wen-rui Dng et al. FIG. 5 Angular dependene f the prdut energy dispsal. The rrespnding llisin energies are: 5.43 kj/ml (a), 6.69 kj/ml (b), 7.77 kj/ml (), 8.69 kj/ml (d), 9.95 kj/ml (e), 11.2 kj/ml (f), 12.7 kj/ml (g), 14.5 kj/ml (h), 16.8 kj/ml (i), and kj/ml (j). f r, f v, and f t. 2 1 (a) 1 5 (b) 1 () ο (d) FIG. 6 Vibratinal-reslved llisin energy-dependent DCS. (a) v=, (b) v=1, () v=2, and (d) v=3. tatinal energy dispsal is nt strngly dependent n the sattering angles in the whle llisin energy regin studied in this wrk. As the llisin energy inreases, the f r nly ges up slwly as the sattering angle hanges frm frward t bakward. At mst llisin energies, f v ges dwn as the sattering diretin hanges frm frward t bakward; while f t ges up. In mparisn with Ref.[16], the tw sets f results at llisin energies higher than kj/ml are quite similar. D. Cllisin energy dependent differential rss setins The reatin resnane in the F+HD HF+D reatin at llisin energies lwer than 5.43 kj/ml plays a dminant rle [24, 26 28]. One main feature f the resnane is the frward sattering f the HF prdut. It is therefre interesting t see hw angular distributin f different HF vibratinal state prdut hanges with the llisin energy larger than 5.43 kj/ml and hw the frward and bakward sattering HF prduts DOI:1.188/ /24/5/ Chinese Physial Siety

7 Chin. J. Chem. Phys., Vl. 24, N. 5 Crssed Mleular Beams Study n the F+HD HF+D (a) (b) () ο FIG. 7 Cllisin energy dependent DCS f the HF(v =2), j = 4 (a), 5 8 (b), and 9 13 (), respetively. vary with the llisin energy. In the experiment, we have measured the bakward sattering HF signals at different llisin energies, therefre all DCS an be nneted relatively. Figure 6 shws the llisin energydependent DCS fr different HF vibratinal state prdut. Fr HF(v =3), the prdut is dminantly frward sattered with sillatry strutures as the llisin energy hanges. The frward sattering prdut at high llisin energy fr the v =3 HF prdut is very interesting. Whether this is related t the Feshbah resnanes [26, 27, 29] remains t be investigated. The HF(v =2) prdut is very different frm HF(v =3), it nly shws a frward peak at llisin energies belw 8.36 kj/ml. This frward peak is very likely related t the Feshbah resnanes. At higher llisin energies, the HF(v =2) prdut are mainly sattered in the bakward sideway diretin, whih is prbably due t diret reatin mehanism [16, 26, 27, 29]. Fr HF(v =1), there are sme small frward sattering signal, as llisin energy inreases, this frward sattering signal diappeared. The frward sattered signal at lw llisin energy shuld als be related t the Feshbah resnane at the lw llisin energies. At higher llisin, the prdut is dminantly bakward sattering, whih is likely due t the diret reatin mehanism. The HF(v =2) prduts at all the llisin energies are fully r at least partially rvibratinal state reslved, therefre, hw resnane affets prdut rtatinal distributin an be investigated in detail. In Fig.7, the llisin energy dependent DCS f HF(v =2) fr three different rtatinal ranges: j = 4, 5 8, 9 13, are shwn. It is very interesting that different HF(v =2) rtatinal states shw very different angular distributins and energy dependene. The HF(v =2) prdut in the j = 4 range shws the biggest frward sattering at the lw llisin energy, and it ges dwn quikly as the llisin energy inreases. The HF(v =2) prdut in the j =5 8 range shws similar behavir. Fr the HF(v =2) prdut in the j =9 13 range, the frward sattering signal ges up and dwn twie, whih is very intrguing. Theretial studies fr this behavir is learly needed t explain this interesting phenmenn. IV. CONCLUSION In this wrk, we perfrmed high reslutin rssed mleular beam experiment n the F+HD reatin at ten llisin energies ranging frm 5.43 kj/ml t kj/ml using the D-atm Rydberg tagging timef-flight tehnique. Quantum state reslved differential rss setins have been measured. Frm the prdut DCS, we bserved the bakward prdut f the HF(v =2) shift t the sideway as the llisin energy inreased, while the frward prdut lse their intensity gradually in this press. Fr the HF(v =3) prdut, the frward satterings are always dminant ne the llisin energy is abve the threshld f this hannel. The HF(v =) and HF(v =1) prduts are mstly sattered in the bakward diretin with nly a small amunt f HF(v =1) in the frward diretin. We have als mpared with the results f the rssed beams experiment in Ref.[16]. There are lear differenes between ur results and thse f Lee et al. [16]. This is prbably due t the different experimental nditins in the tw experiments, as well as the different detetin methd. Vibratinal branhings f the HF prdut have been determined in the urrent experiment. As the llisin energy inreases, the relative ppulatin f the HF(v =) and HF(v =1) prdut inreases, while that f HF(v =2) and HF(v =3) dereases. In the prdut energy dispsal, f r ges up gradually frm frward t bakward beause the main prdut in the bakward diretin are rtatinally htter than that f the frward ne averagely. The f v inreases with shift frm sideway t the frward diretin. Fr the HF(v =2) prdut at llisin energies lwer than 8.36 kj/ml, frward sattering are mstly lw j prdut, while at higher llisin energies higher rtatinal exitatin in HF(v =2) is bserved in the frward satering. This set f dynamial results fr the F+HD HF+D reatin is quite mplete and it prvides a gd testing grund fr theretial understanding f the interesting dynamis at the high llisin energies fr this benhmark system. DOI:1.188/ /24/5/ Chinese Physial Siety

8 514 Chin. J. Chem. Phys., Vl. 24, N. 5 Wen-rui Dng et al. V. ACKNOWLEDGMENTS This wrk was supprted by the Chinese Aademy f Sienes, the Natinal Natural Siene Fundatin f China, and the Ministry f Siene and Tehnlgy f China. [1] G. C. Shatz, J. M. Bwman, and A. Kuppermann, J. Chem. Phys. 63, 674 (1975). [2] G. C. Shatz, J. M. Bwman, and A. Kuppermann, J. Chem. Phys. 63, 685 (1975). [3] S. F. Wu, B. R. Jhnsn, and R. D. Levine, Ml. Phys. 25, 839 (1973). [4] D. M. Neumark, A. M. Wdtke, G. N. Rbinsn, C. C. Hayden, and Y. T. Lee, Phys. Rev. Lett. 53, 226 (1984). [5] D. M. Neumark, A. M. Wdtke, G. N. Rbinsn, C. C. Hayden, and Y. T. Lee, J. Chem. Phys. 82, 345 (1985). [6] D. M. Neumark, A. M. Wdtke, G. N. Rbinsn, C. C. Hayden, K. Shbatake, R. K. Sparks, T. P. Shafer, and Y. T. Lee, J. Chem. Phys. 82, 367 (1985). [7] J. F. Castill, D. E. Manlpuls, K. Stark, and H. J. Werner, J. Chem. Phys. 14, 6531 (1996). [8] K. Stark and H. J. Werner, J. Chem. Phys. 14, 6515 (1996). [9] F. J. Aiz, L. Banares, V. J. Herrer, V. S. Rabans, K. Stark, and H. J. Werner, Chem. Phys. Lett. 223, 215 (1994). [1] A. Weaver and D. M. Neumark, Faraday Disuss. 91, 5 (1991). [11] S. E. Bradfrth, D. W. Arnld, D. M. Neumark, and D. E. Manlpuls, J. Chem. Phys. 99, 6345 (1993). [12] D. E. Manlpuls, K. Stark, H. J. Werner, D. W. Arnld, S. E. Bradfrth, and D. M. Neumark, Siene 262, 1852 (1993). [13] Y. T. Hsu, K. Liu, L. A. Pedersn, and G. C. Shatz, J. Chem. Phys. 11, 7921 (1999). [14] J. H. Wang, Y. T. Hsu, and K. Liu, J. Chem. Phys. 11, 6593 (1997). [15] S. H. Lee, F. Dng, and K. Liu, J. Chem. Phys. 116, 7839 (22). [16] S. H. Lee, F. Dng, and K. Liu, J. Chem. Phys. 125, (26). [17] M. H. Qiu, Z. F. Ren, L. Che, D. X. Dai, S. A. Harih, X. Y. Wang, X. M. Yang, C. X. Xu, D. Q. Xie, M. Gustafssn, R. T. Skdje, Z. G. Sun, and D. H. Zhang, Siene 311, 144 (26). [18] M. H. Qiu, Z. F. Ren, L. Che, D. X. Dai, S. A. Harih, X. Y. Wang, and X. M. Yang, Chin. J. Chem. Phys. 19, 93 (26). [19] L. Che, Z. F. Ren, X. G. Wang, W. R. Dng, D. X. Dai, X. Y. Wang, D. H. Zhang, X. M. Yang, L. S. Sheng, G. L. Li, H. J. Werner, F. Lique, and M. H. Alexander, Siene 317, 161 (27). [2] Z. F. Ren, L. Che, M. H. Qiu, X. G. Wang, D. X. Dai, S. A. Harih, X. Y. Wang, X. M. Yang, C. X. Xu, D. Q. Xie, Z. G. Sun, and D. H. Zhang, J. Chem. Phys. 125, (26). [21] X. G. Wang, W. R. Dng, M. H. Qiu, Z. F. Ren, L. Che, D. X. Dai, X. Y. Wang, X. M. Yang, Z. G. Sun, B. N. Fu, S. Y. Lee, X. Xu, and D. H. Zhang, Pr. Natl. Aad. Si. USA 15, 6227 (28). [22] W. R. Dng, C. L. Xia, T. Wang, D. X. Dai, X. M. Yang, and D. H. Zhang, Siene 327, 151 (21). [23] C. Xu, D. Xie, and D. H. Zhang, Chin. J. Chem. Phys. 19, 96 (26). [24] Z. F. Ren, L. Che, M. H. Qiu, X. A. Wang, W. R. Dng, D. X. Dai, X. Y. Wang, X. M. Yang, Z. G. Sun, B. Fu, S. Y. Lee, X. Xu, and D. H. Zhang, Pr. Natl. Aad. Si. USA 15, (28). [25] M. H. Qiu, L. Che, Z. F. Ren, D. X. Dai, X. Y. Wang, and X. M. Yang, Rev. Si. Instrum. 76, 1612 (25). [26] R. T. Skdje, D. Skuteris, D. E. Manlpuls, S. H. Lee, F. Dng, and K. Liu, J. Chem. Phys. 112, 4536 (2). [27] R. T. Skdje, D. Skuteris, D. E. Manlpuls, S. H. Lee, F. Dng, and K. Liu, Phys. Rev. Lett. 85, 126 (2). [28] F. Dng, S. H. Lee, and K. Liu, J. Chem. Phys. 113, 3633 (2). [29] S. H. Lee, F. Dng, and K. Liu, Faraday Disuss. 127, 49 (24). DOI:1.188/ /24/5/ Chinese Physial Siety