The use of laser excitation in the study of the absorption of two photons for chla was reported by Terenin (1968) and Liu Yixian (1981). This paper reports the fluorescence spectra of the higher excited singlet state for chla solution in n-pentane excited by xenon lamp (430nm)

and the fluorescence excitation spectra.When centre emitting mode was applied to excited sample of chla solution (see Fig. la) the fluorescence of chla solution in the concentration range of 10

-4

-10

-3

M at 300K excited by 430nm shows emission bands at about 665nm and 720nm

and in the concentration range of 10

-7

-10

-5

M

it shows emission band at about 493nm. The intensity rate of 665nm to 493nm is about 100(see Fig.2).However

when surface emitting mode was applied to excited sample of chla (see Fig.1b)

the fluorescence of chla solution in the concentration range of 10

-7

-10

-5

M at 300K excited by 430nm shows emission bands at 520nm and 580nm

and it shows emission band at about 665nm only in the higher concentration range of 10

-5

-10

-3

M (see Fig.3). When sample was frozen to 77K excited by 430nm

its fluorescence shows emission bands at about 520nm

580nm

665nm and 720nm (see Fig.4).Absorption spectra and excitation spectra of chla were measured. Excitation spectrum of the fluorescence at 665nm coincides with absorption spectrum for chla. Two principal absorption peaks are at about 430nm and 660nm(see Fige.5e).The excitation spectrum of the fluorescence at 493nm shows peaks at 354nm and 430nm(see Fig.5a)

while excitation spectrum of the fluorescence at 520nm shows peak at 430nm (see Fig

5b) and excitation spectrum of the fluorescence at 580nm shows pea- ks at 430nm and 490nm (see Fig.5c). It can be seen from the experimental results that the reabsorption of chla solution was minimized due to the use of surface emitting mode. So that the fluorescence at 520nm and 580nm was measured from transition of the higher excited singlet state S

2

to the ground state S0. And weaker fluorescence at 493nm from transition S

2

-S

0

was measured by higher detection sensitivity. From the experimental results processes of electronic transition in chla can be shown by the schematic energy level diagram in Fig. 6.