REACTION DYNAMICS OF ATOMS AND MOLECULESUSING THE PULSE CHARACTER OF. SYNCHROTRON RADIATION
Yoshihiko Hatano
Department of Chemistry, Tokyo Institute of Technology,Meguro-ku, Tokyo 152
1. Introduction
Synchrotron radiation(SR) is generally known as a pulsed,
stable and tunable source of VUV radiation. These qualities areexpected to be useful in studying spectroscopic and dynamic
The investigaproperties of highly excited atoms and molecules.
tion has been carried out using mainly electron bombardment.
Recently, however, several time-resolved measurements have been
carried out using the pulse character of SR. 112 > A reaction scheme
actually has become much simpler using SR than electrons. An
analysis of the experimental results thus becomes easier, and more
Table 1 shows the pulse-to-pulse interval of SR and thereliable.
corresponding experiments in single bunch operation at main facilities in the world. 3 >The SOR-RING 4 >at SRL-ISSP has recently been successful insingle-bunch operation, where the time interval between two pulses
is 58ns. 5 > The first attempt at using the pulse character of SR
from the SOR-RING has been successful recently and shown clearly
that SR is a promising tool for studying reaction dynamics ofstate-specified highly excited atoms and molecules. 21
2. Time-Resolved Investigation of the De-excitation of Xenon
Exclmer by SF 6 and N 2 2)Time resolved fluorescence from vibrationally relaxed Xe2*(ou+) excimer states has been observed in the selective excitation
by SR pulses of Xe2(og+) van der Waals molecules in the presenceof quencher molecules.
Synchrotron radiation isThe apparatus is shown in Fig.l.
dispersed by a l.Om Seya-Namioka monochromator with a 600 line/mm
Dispersed light passes through an exit slit (2.5nm bandgrating.
pass for the maximum slit width) and enters a gas cell through aThe fluorescence of the second continuum emission
MgF2 window.
was measured by conventional single-photon counting with a delayedcoincidence technique and accumulated in a MCA for several minutes.
The decay rate in the intensity of the second continuum
emission was observed on the red-wing excitation of xenon gas withvarious partial pressures of a quencher molecule. The results areshown in Fig.2. The slope of the straight line gives the deexcitation rate constant of Xe2*(ou+, low v) for SFG or N2,
respectively as 9Xl0- 10 cm 3 /s (300A 2 ) and 7xl0- 12 cm 3 /s (2A 2 ). The
magnitude of the obtained values shows a striking contrast witheach other.
3. Fluorescence Lifetime Measurements of Liquid Hydrocarbons 6 >An attempt of fluorescence llfetlme measurements of llquidsaturated hydrocarbons has been made with the following purposes:
1) To observe extremely weak fluorescence induced by SR pulses.
The success in this observation will assure us of the usefulnessof SR pulse character generally in measuring very weak signals2) To determine thefrom scientifically important systems.
fluorescent lifetime of liquid saturated hydrocarbons. The lifetime values have been obtained using a variety of pulsed excita-171-

tion sources; ordinary X-ray tubes, H2 lamps, N 2 lasers, electronbeams, etc. 7> The usefulness of SR in such measurements wasexpected earlier. 8 > SR could be a new and the best excitation
source whose energy can be selected continuously in the wide rangeof wavelength.
This is the first attempt to measure the fluorescence lifetime of liquid saturated hydrocarbons by SR.
The experimental apparatus was almost the same as that in
Fig.l.
The sample purification method was similar to that usedin the electron mobility measurements. 9> Fluorescence lifetime
measurements were carried out at several excitation wavelength.
In the case of cyclohexane, the FWHM of the fluorescence decay
profile was only a little larger than that of the apparatus
function, while in the case of bicyclohexyl two distinct fluorescence decay curves were observed as shown in Fig.3. The contribution of slow decay became larger in the wavelength region longer
than about 180 nm.
In the shorter wavelength region, the fluorescence showed only fast decay.
It is a very interesting phenomenon
although the reason is not known yet. As far as the signal
intensity was concerned, it was clearly found that the SR light
produced in the single bunch operation of the SOR-RING was strong
enough for the present experiment dealing with the very weakfluorescence.
The fluorescence lifetime of sodium salicylate, a very usefulwave-shifter or scintillator, has been tentatively measured using
SR pulses. The result is shown in Fig.4. The obtained lifetime
value, 4 nsec, is considerably shorter than those previously
reported.
Since this compound will be widely used also in thefuture for synchrotron radiation research, such measurements
should be carefully carried out in detail.
Referencesl) 0. Dutuit, R. A. Gutcheck and J. le Calv~, Chern. Phys. Letters58, 66 (1978); H. D. Wenck, S. S. Hasnain, M. M. Nikitin, K.
Sommer, G. Zimmerer and D. Haaks, ibid., 66, 138 (1979); 0.
Dutuit, M. C. Castex, J. le Calv~ and M. Lavoll~e, J. Chern.
Phys., 73, 3107 (1980); T. D. Bonifield, F. H. K. Rambow,
G. K. Walters, M. V. McCusker, D. C. Lorentz and R. A. Gutchek,ibid.' 72, 2914 (1980).
2) Y. Hatano, M. Ohno, N. Kouchi, H. Koizumi, A. Yokoyama, G.
Isoyama, H. Kitamura and T. Sasaki, Chern. Phys. Lett., 84,454 (1981).
3) Y. Hatano, KEK Report "Proc. Meeting on Pulse Structure of SR
and its Applications" ed. by Y. Hatano and T. Ohta, KEK 81-16(1982), p.32.
4) T. Miyahara, H. Kitamura, S. Sato, M. Watanabe, S. Mitani,
E. Ishiguro, T. Fukushima, T. Ishii, Shi. Yamaguchi, M. Endo,
Y. Iguchi, H. Tsujikawa, T. Sugiura, T. Katayama, T. Yamakawa,Se. Yamaguchi and T. Sasaki, Particle Accelerators, 7, 163(1976).
5) H. Kitamura, G. Isoyama, A. Uchida, S. Sato and T. Yamakawa,
Activity Report of SRL-ISSP-1979, 95 (1980).
6) N. Kouchi, K. Shinsaka, Y. Nakamura, M. Toriumi, H. Koizumi,T. Tezuka, N. Takahashi, M. Ukai, S. Yano, G. Isoyama, Y.
Hatano and T. Sasaki, Activity Report of SRL-ISSP-1980, 46(1981).
7) Y. Katsumura, S. Tagawa andY. Tabata, Radiat. Phys. Chern.,
in press.
8) T. Wada andY. Hatano, J. Phys. Chern., 81, 1057 (1977).
9) T. Wada, K. Shinsaka, H. Namba andY. Hatano, Can. J. Chern.,
55, 2144 (1977).
-172-Table 1.

Facilities

SK Pulse St~ucture and thein Single Bunch OperationPulse-t.o-?ulse*Inter-val (nsec)

TOF

Fluorescence

Ion dissociation
H...~..., ,o-r-' ,H o~ etc.
2 2 2

Hemoglobin,fluorescein

73

ACO

Ex~eriQentsnaohthol,)rO,CO,etc.

Xe~,3iologicallyim9ort.ant compounds
Kr;,xe;,solids

1000

DORIS

*2 , etc.
*XeF,XeF
SPEAR* * *2
Xe,Kr,xe780

Solid surface
Ion desorDtion
Angle resOlved
electr-ons

Proteins(Polarized SR)*~~f~~-:~~;~~~i~~ion

58

SOR-RING

Liquid hydrocarbons

Electr-onic quenchingof radic-:tlsPF624

NSLS (VUV)170

UVSOR170* Pulse width = rv 102 psec

1·~ 0.6'p 0.4I1sF6Pxe 500 Torr155 nm
151 nm1,;
or-al"-----"0Q.

20

N240150 nm

80( Torr J60

Fig. 1 • Schmatic diagram of the app,.ratus

100

Fig.2. Observed decaying ratesof the second continuum
emission under red-wing
excitation as a functionof the pressure of SF 6
and N2 .

%·-o~v-3l~...~:vl>'--i:'-...'·.-~.

t

1° 1 0~-L~,0~~-.to~~~,~o--L-oa~o--~>~o~o_J-,.l~1no_J
CHANNEL NUMBERFig.3. Time-resolved fluorescenceof liquid bicyclohexyl
at 230 nm excitation (17°C).
+--- Fig.4. Observed fluorescence decayof sodium salicylate.

lnsee-173-