USAGE OF LASER RAMAN SPECTROSCOPY TO INDENTIFY THE UNSTABLE

In this work laser Raman Spectroscopy was used to identify the unstable compounds in three iron oxides. These samples were irradiated using 5mW frequency doubled Nd laser with 532 nm at room temperature. Spectra database was used for the spectral analysis of the Raman shift of the three samples. The results obtained showed that the unstable compounds appeared in the spectra of the samples. appeared in the spectra of goethite and akaganeite compounds while magnetite compounds appeared in the spectra of hematite. The laser power causes the bands to broaden and to undergo a small shift to lower wavenumbers. Other materials are three samples like disulfide, alkyl disulfide and aliphatic fluoro proved to be suitable method for the identification of unstable compounds in hematite, goethite and akaganeite and could be used for other materials


INTRODUCTION
Raman spectroscopy is a spectroscopic technique used in condensed matter physics and chemistry to study vibrational, rotational and other low-frequency modes in a system [1]. It depends on the scattering phenomenon. In this context, scattering occurs due to collisions between photons and molecules. Generally, a photon collides with a substance, not necessarily only with a molecule. Irradiation of light with the frequency v 0 upon a certain molecule bring photons with the energy E = hv 0 to this molecule. photons colliding with molecules do not change their energy after the collision (elastic collision) and the ensuing radiation is called Rayleigh scattering. Rayleigh scattering consists photons that have the same frequency as the incident light. A very small number of the photons that collide with the molecules exchange energy with them upon the collision (an example of in elastic collision). If an incid delivers an hv 0 quantum of energy to the molecule, the energy of the scattered photon reduces to h(v 0 -v) and the frequency of the scattering photon becomes (v 0 -v). On the contrary, when an incident photon receives the hv energy from the molecule, the energy of the scattering photon rises to and the frequency of the scattering photon becomes Scattering in which an incident photon exchanges energy with a molecule is known as Raman scattering [2]

A B S T R A C T
In this work laser Raman Spectroscopy was used to identify the unstable compounds in three iron oxides. These samples were irradiated using 5mW frequency doubled Nd laser with 532 nm at room temperature. Spectra database was used for the spectral analysis of the Raman shift of the three samples. The results obtained showed that the unstable compounds appeared in the spectra of the samples. appeared in the spectra of goethite and akaganeite compounds while magnetite compounds appeared in the spectra of hematite. The laser power causes the bands to broaden and to undergo a small shift to lower wavenumbers. Other materials are three samples like disulfide, alkyl disulfide and aliphatic fluoro proved to be suitable method for the identification of unstable compounds in hematite, goethite and akaganeite and could be used for other materials Raman spectroscopy is a spectroscopic technique used in condensed matter physics and chemistry to study vibrational, frequency modes in a system [1]. It phenomenon. In this context, scattering occurs due to collisions between photons and molecules. Generally, a photon collides with a substance, not necessarily only with a molecule. Irradiation of light with the upon a certain molecule brings a number of to this molecule. Most photons colliding with molecules do not change their energy after the collision (elastic collision) and the ensuing radiation is called Rayleigh scattering. Rayleigh scattering consists of photons that have the same frequency as the incident light. A very small number of the photons that collide with the molecules exchange energy with them upon the collision elastic collision). If an incident photon quantum of energy to the molecule, the energy and the frequency . On the contrary, v energy from the , the energy of the scattering photon rises to h(v 0 +v), and the frequency of the scattering photon becomes (v 0 +v). Scattering in which an incident photon exchanges energy with s known as Raman scattering [2].
Scattered light having the frequency of the frequency of vibration v 0 scattering'' and ''anti-Stokes Raman scattering'', respectively. Stokes Raman scattering arises from interaction between a photon and a molecule that is in the ground state, while anti-Stokes Raman scattering is due to interaction between a photon and a molecule that is in the excited state [2]. At ambient temperatures, most molecular vibrations are in the ground state and thus the anti likely to occur than the Stokes transitions, resulting in the Stokes Raman scattering being more intense. For this reason, it is usually the Stokes Raman spectrum that is routinely studied [3]. Actually it is the finger print of the molecule so it can be used to identify different ma use Raman Spectroscopy to identify the unstable compounds of three types of the iron oxides.

MATERIALS AND METHODS
Three samples of hematite, goethite and akaganeite, were investigated in this work by laser Raman range from 400 cm -1 to 4500 cm

Equipments
In this work laser Raman microscope Burker sentrra, shown in the source of this spectrometer is Nd of 532 and output power of 5mW. The Raman shift in wave number, and the change in intensities in of the scattered light were compared with data in the references and previous studies. In this work laser Raman Spectroscopy was used to identify the unstable compounds in three iron oxides. These samples were irradiated using 5mW frequency doubled Nd-YAG Spectra database was used for the spectral analysis The results obtained showed that the unstable of the samples. Characteristic bands of hematite ppeared in the spectra of goethite and akaganeite compounds while magnetite compounds The laser power causes the bands to broaden and to materials are appeared in spectra of the disulfide, alkyl disulfide and aliphatic fluoro. Raman spectroscopy the identification of unstable compounds in hematite, ld be used for other materials.
Scattered light having the frequency of v 0 -v and that having 0 +v are called ''Stokes Raman Stokes Raman scattering'', respectively. Stokes Raman scattering arises from interaction between a photon and a molecule that is in the ground state, Stokes Raman scattering is due to interaction between a photon and a molecule that is in the excited state At ambient temperatures, most molecular vibrations are in the ground state and thus the anti-Stokes transitions are less n the Stokes transitions, resulting in the Stokes Raman scattering being more intense. For this reason, it is usually the Stokes Raman spectrum that is routinely it is the finger print of the molecule so it ferent materials. This work aimed to Raman Spectroscopy to identify the unstable compounds of three types of the iron oxides.

MATERIALS AND METHODS
Three samples of hematite, goethite and akaganeite, were investigated in this work by laser Raman spectrometer in the to 4500 cm -1 .
In this work laser Raman microscope spectrometer model Burker sentrra, shown in the Figure (1) was used. The light source of this spectrometer is Nd-YAG laser with wavelength output power of 5mW. The Raman shift in wave number, and the change in intensities in of the scattered light were compared with data in the references and

Samples preparation
Samples were prepared as follows

Sample1: Hematite (Fe 2 |O 3 )
Fourty grams of Ferric nitrate (Fe (N0 3 ) 3 . 9 H 2 0) was dissolved in 500 ml of twice distilled water in polyethylene flask. Then , 300 ml of one molar (1M) potassium hydroxide (KOH) was added to the flasked followed by 50 ml of one molar (1M) sodium bicarbonate (NaHCO 3 ) . The mixtures were heated to 90C 0 , till formation of red brown precipitates of ferrihydrite. The flask and the content was allowed to stand for 48 hours. During this time the red brown suspension of ferrihydrite transformed to hematite with pH of 8 to 8.5 [4].

Sample2: Goethite( FeOOH)
100 ml of one molar (1M) Ferric nitrate (Fe(N0 3 ) 3 solution was added into 2 liter polyethylene flask, then 180 ml of five molar (5M) potassium hydroxide (KOH) was added rapidly with stirring, till formation of Red brown precipitates of ferrihydrite at once. The suspension was diluted with twice stilled water and holded in a closed polyethylene flask maintained at 70 C 0 in an oven for 60h. At the end of this period of time the red-brown suspension of ferrihydrite transformed in to a compact yellow precipitate of goethite [5].

Sample 3: Akaganeite( FeOOH)
0.1 molar (0.1M) of FeCl 3 solutions hold in to 2 liter in closed vessel at 70C 0 for 48h. During this time the pH of the system drops from 1.7 to 1.2 and compact yellow precipitate of akaganeite was formed [5]. Figure (2) shows the Raman spectrum of hematite after irradiation with Nd-YAG laser with wavelength of 532 nm and 5mW output power. The spectrum shows clear peaks and by comparison with the vibrations recorded in some references we found that these vibrations are attributed to hematite compounds beside unstable components of hematite and some components of materials that are listed in table (1).      Through the analysis of the three samples it was found that the vibration modes of some materials are appeared as follows:  [ 10,11] . Also vibrational modes at 713 cm -1 , 660 cm -1 and 323 cm -1 were observed. These are assigned to Magnetite and this agreed with the results of other research (Shebanova ON et al. 2003, Oh et al. 1998) [13,14]. Vibration modes of other materials are observed at 464 cm -1 and assigned to silicate, 685 cm -1 assigned to alkyl sulfides, 514 cm -1 assigned to dialkyl disulfide, 774 cm -1 and 784 cm -1 which are assigned to Aliphatic fluoro according to [6.7.8.9].

RESULTS AND DISCUSSION
In the Raman spectrum of Goethite high intensity vibrational modes of α Fe-OH are appeared at 389 cm -1 , 235, 302.2, 389, 471, 560 and 681 cm -1 and are assigned to goethite as mentioned in the literatures (Oh et al. 1998) [14 ] . Also we found vibrations mode of FeII-O that appeared in the spectra at 702 and 613 cm -1 and assigned to hematite and mentioned in the literatures (Thibeau et al. a 1978, De Faria al. a 1997), [10,11]. Other vibration modes at 538 cm -1 and assigned to silicate, vibration mode at 641 cm -1 attributed to alkyl disulfide and mode at 741 assigned to aliphatic fluoro and those findings agreed with the results of other research's [6.7.8.9] . For akaganeite, seven vibration modes of βFe-OH appeared at 302, 385, 708 cm -1 , 490, 533, 612 and 670 cm -1 are assigned to akaganeite as presented in the literatures (Oh et al.1998) , [14] . In addition vibration modes at 215 and 258 cm -1 are recorded which attributed to hematite according to (Thibeau et al. a 1978, De Faria al. a 1997, [10,11]. Other vibration modes were observed at 448 cm -1 and assigned to dialkyl disulfide, 579 cm -1 and assigned to alkyl disulfide, 773 cm -1 and assigned to aliphatic fluoen according to [6,7,8,9].

CONCLUSIONS
The results presented in this work show that Raman spectroscopy technique is an efficient method to identify unstable compounds of hematite, goethite and akaganeite. It provides precise information about other materials found in the three samples.  Table 3 The analyzed data of Raman spectrum of the akaganeite