Langmuir-Blodgett (LB) films of arachidic acid have been used as spacer layers to control the separation distance between evaporated In and Ag metal island films and LB monolayers of a lightly substituted phthalocyanine. From relative intensity measurements, the distance dependence of the surface-enhanced Raman scattering (SERS) enhancement factor for the phthalocyanine was determined and found to be long range. In addition the magnitude of the enhancement was determined by measurement of the normal Raman intensity of phthalocyanine monolayers deposited directly onto unmetalized substrates. The results are compared with calculations of the enhancement factor based on an electromagnetic field enhancement mechanism. Good quantitative agreement is found between calculation and experiment for both the distance dependence and magnitude of the enhancement. We conclude that our SERS from island films is due to the electromagnetic mechanism and rule out short-range chemical mechanisms.

guishing high and low Si/Al ratio zeolites and may be important in studies of zeolites that are chemically or physically altered.Acknowledgment. The support of the National Sci-ence Foundation under Grant CHE 8204417 is gratefully acknowledged. We thank Professor T.

No abstract

Thin solid films of Mg, Cu and Zn phthalocyanine complexes have been studied using Raman spectroscopy. Laser excitation lines near resonance and in resonance with the electronic absorption band of the substrate have been used. A description of vibrational modes is given and correlations in vibrational properties of the series are discussed.Metallated phthalocyanines are well known for their industrial applications. Recently, the photovoltaic properties of phthalocyanine (Pc) and its metal complexes have been the object of intensive research. As a result, thin-film photovoltaic devices have been reported for MgPc,"' ZnPc3 and C U P C .~ These developments prompt the study of molecular properties, polymorphic forms and the molecular-metal interactions at the thin film-metal interface. Molecular structure determinations by X-ray diffraction methods indicate that the phthalocyanate ligand constrains the Zn, Cu and Mg atoms to effectively square-planar c~o r d i n a t i o n .~'~ It has also been suggested that the difference between various polymorphic forms is due to octahedral coordination of the metal atom to different nitrogen atoms of neighbouring macrocycles. This hypothesis seems to be supported by two independent observations. Firstly, from the chemistry of CuPc it is known that the a-polymorph is readily obtained by treating the P-polymorph with sulphuric acid, thus blocking the nitrogen atoms with sulphate residues. Secondly, Sauvage and De B a~k e r ,~ in their infrared studies, have observed that the (3-polymorph of ZnPc and MgPc exposed to formic acid vapours form a complex and also undergo P+a polymorphic transformation.In this paper, molecular vibrational frequencies of Zn, Cu and MgPc observed in the Raman spectra are reported and characteristic group frequencies are discussed. ~ EXPERIMENTAL The Mg, Cu and Zn phthalocyanine complexes were deposited from a tantalum boat on to a tin-oxide (NESA) glass and on to quartz in a Varian NRC 3115 vacuum system at a pressure of 5 x lop7 Torr. Thicknesses of about 100 and 200nm for all films were monitored with an Inficon XTM quartz crystal oscillator. The Spectra-Physics Ar+ laser (Model 164) and a 375 t For Part 2 see Spctrochirn. Acta, Pan A 39, 847 (1983).$ Author to whom correspondence should be addressed. dye laser were used for excitation of solid films. The surface film and the incident laser line were at a ca 30" angle. Scattered light was analysed using a Spex 14018 double monochromator with 1800 lines mm-' holographic gratings and detected by a cooled Hamamatsu R955 photomultiplier, followed by conventional photon counting. The spectral slit width was 6 cm-'. Absorption spectra were recorded on a Cary 17 spectrophotometer. RESULTS AND DISCUSSIONRaman spectra (RS) of MgPc, CuPc and ZnPc in the a-polymorphic form are shown in Fig. 1. The exciting radiation frequency 514.5 nm falls within the valley of the absorption spectra formed by the Soret and the red band, hence these are preresonance RS. Considering that the molecular structure of all the phthalocy...

No abstract