Study of Absorption and Fluorescence Spectra of

Iodomethane Molecules by Solvent Effect

F Yao, N Ning, J H Li, Y Wang, Y J Zhai and W H Fang

Key Laboratory of Nanohotonics and Biophotonics of Jilin Province, School of Scie

nce, Changchun University of Science and Technology, Changchun 130022, China

Corresponding author and e-mail: W H Fang, whfang@cust.edu.cn

Abstract.The absorption spectra and fluorescence spectra and their haracteristics of

iodomethane (CH

I) excited by ultraviolet light were analyzed experimentally. It was found

that methyl iodide had a good absorption of 280-375 nm ultraviolet light and obvious

fluorescence was emitted at 280-320 nm ultraviolet light excitation; CH

I-toluene mixed

solutions with different ratio on volume were excited at the light with the wavelength of

300nm. It was found that the fluorescence intensity gradually increased with the increase of

toluene volume ratio and a basic linear relationship was shown. We also measured the

fluorescence spectra of the CH

I-ethanol mixed solutions at different wavelengths of

ultraviolet light, and variation of the fluorescence intensity of the CH

I-ethanol solutions

with different mixing ratio is also different. In additional, we are giving the mathematical

expression of the fluorescence peak position of the mixed solution. This give some reference

significance of the solvent effect and the study of CH

I molecular dynamics by the spectrum.

1. Introduction

In the industrial field, CH

I is an important downstream industrial product of coal chemical industry.

It is also a precursor of many methylation reactions [1, 2]. CH

I is a typical molecular theoretical and

experimental model in the laboratory, which plays an important role in the kinetics of photolysis [3, 4]

and thermal cracking. However, CH

I is easily decomposed by heat and can produce toxic iodide flue

gas, which can be absorbed by respiratory tract, digestive tract and skin, so it is very important for

quantitative analysis. At present, the quantitative analysis by gas chromatography [5] is an analytical

method widely used in analytical laboratories. This method determines the content of the components

to be measured in a sample. Standard samples are also useful for spectrophotometric analysis of trace

amounts of CH

I. Based on the molecular fluorescence spectrum analysis (MFS)[6]

is the use of

certain substances produced by ultraviolet or visible light irradiation after can reflect the material

characteristics of the fluorescence, and carries on the qualitative and quantitative analysis, is widely

used and the promising a spectrum analysis technology. Using this technique, we studied the

corresponding absorption and fluorescence spectra [7, 8, 9] of CH

I. The results showed that CH

I [9]

can emit strong fluorescence under the excitation of 280-320 nm UV light. The fluorescence

characteristics were characterized in this paper.

Yao, F., Ning, N., Li, J., Wang, Y., Zhai, Y. and Fang, W.

Study of Absorption and Fluorescence Spectra of Iodomethane Molecules by Solvent Effect.

In Proceedings of the International Workshop on Materials, Chemistry and Engineering (IWMCE 2018), pages 519-529

ISBN: 978-989-758-346-9

519

2. Experimental device and experimental method

2.1. A subsection experimental device

The absorption spectrum of this experiment is based on the Gary 5000 UV-Vis-NIR

spectrophotometer, light source: xenon lamp, mercury lamp, among which the mercury lamp is used

for wavelength calibration to ensure the accuracy of the instrument for long-term use of the

wavelength, and the three light sources are automatically switched. Monochromator: Heteropoly

Littorow monochromator, dual monochromator design. Detectors: High-sensitivity photomultipliers

and semiconductor-cooled PbS. The fluorescence spectrum was measured using a Gary Eclipse

fluorescence spectrophotometer with a horizontal light source: a flashing xenon lamp with a pulse

width at half maximum of less than 2 microseconds, a power relative to 75 kW when continuously

illuminated, and a Cheney-Turner monochromator, ultra low Stray light.

2.2. Reagents

The CH

I, toluene and ethanol used in the test were all manufactured by AKCO Reagents. In the

experiment, CH

I was separately mixed with toluene and ethanol as solvents, and the corresponding

concentrations were formulated according to the volume ratio.

2.3. Test methods

When measuring the absorption spectrum of CH

I, toluene is used as a reference. When the

absorption spectrum of a CH

I-ethanol mixed solution is measured, ethanol is used as a reference.

When the absorption spectrum of the CH

I-toluene mixed solution is measured, toluene is used as a

reference. When measuring the fluorescence spectrum of CH

I, the width of the slit is 20 nm, and a

group of excitation light of a control group is selected according to the absorption band, followed by

excitation, and the spectrum is collected.

3. Experimental results

3.1. Absorption spectrum experiment

In this experiment, we used the different volume ratio of CH

I mixed solution to scan the whole

spectrum to get the absorption spectrum.

Figure 1. Absorption spectra of pure CH

I and mixed solutions of CH

I-toluene at different volume

ratios.

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Figure 1 shows that in the spring, CH

I absorbs ultraviolet light from 280 to 375 nm, its

absorbance reaches a maximum at 337 nm, and there is almost no absorption after 375 nm, and the

absorption band width is 298 to 344 nm in luminosity. The process of rapid decline after reaching the

maximum.

Figure 2. Absorption spectra of pure CH

I and mixed solutions of CH

I-ethanol at different volume

ratios.

Comparing the absorption spectra of the CH

I-toluene mixed solution, only four control groups

were given in this experiment. It can be seen from the figure 2 that the ethanol solution has less

influence on the absorption spectrum of CH

I. The absorption peak of the mixed solution shifts blue

as the volume ratio of ethanol solvent increases.

3.2. Fluorescence spectroscopic experiment of CH3I and its mixed solution

3.2.1. CH

I fluorescence spectrum experiment. We use 280-375 nm UV light as the excitation light,

and once every 10 nm [10]. The fluorescence spectrum is found at 280-320 nm UV. As Figure 3

shows that under the UV excitation light of 300nm, the fluorescence intensity of CH

I is the

strongest.

300 350 400 450 500

Intensity/(a.u)

Wavelength/(nm)

280

290

300

310

320

Study of Absorption and Fluorescence Spectra of Iodomethane Molecules by Solvent Effect

521

Figure 3. Fluorescence spectra of CH

I solution under different excitation light.

3.2.2. Fluorescence spectra of CH

I-ethanol solutions at different volume ratios. Under certain

wavelengths of UV excitation, CH

I and ethanol exhibit fluorescence characteristics. Mix the two at

different volume ratios, and excite them with different wavelengths of UV light to find out which

kind of excitation, and which kind of fluorescence ratio is the best. Figures 4(a) to (e) show the

fluorescence spectra of CH3I-ethanol solutions V

in volume ratios of 1:9, 3:7, 5:5, 7:3, and 9:1

respectively, excited by ultraviolet light.

(a)

(b)

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(c)

(d)

Study of Absorption and Fluorescence Spectra of Iodomethane Molecules by Solvent Effect

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(e)

Figure 4. Fluorescence spectra of CH

I -ethanol solutions with different volume ratio under different

excitation light: (a) V1: V2 = 9:1; (b) V1: V2 = 7:3; (c) V1: V2 = 5:5; (d) V1: V2 = 3:7; (e) V1: V2

=1:9.

It can be seen from Figure 4. that with the increase of the volume ratio of ethanol solvent, the

fluorescence peak intensity of the mixed solution increases. When the volume ratio V1:V2 is 5:5

respectively, the fluorescence intensity is the strongest under the excitation light of 290 nm. In other

the fluorescence intensity was the strongest under the excitation light of 300 nm.

3.2.3. Fluorescence spectra of methyl iodide-toluene solution at different volume ratios. Under

different solvents, the fluorescence spectrum of CH

I mixed solution is also one of the topics we

discuss. Figure 5 (a) to (e) respectively show the fluorescence spectra of CH

I-toluene solutions in

volume ratios of 9:1, 7:3, 5:5, 3:7 and1:9, excited by ultraviolet light.

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(a)

(b)

Study of Absorption and Fluorescence Spectra of Iodomethane Molecules by Solvent Effect

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(c)

(d)

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(e)

Figure 5. Fluorescence spectra of CH

I-toluene solutions with different volume ratio under different

excitation light: (a) V1: V3 = 9:1; (b) V1: V3 = 7:3; (c) V1: V3 = 5:5; (d) V1: V3 = 3:7; (e) V1: V3

=1:9.

It can also be seen from Figure 5. when the mixing ratio of 9:1, the fluorescence intensity is the

strongest under the irradiation of light with 300 nm.

In order to better demonstrate the effect of different volume ratio of mixed solution on the

fluorescence intensity and the position change corresponding to the strongest peak of fluorescence,

we chose 300nm excitation light to act on CH

I-toluene mixed solution to obtain the curve of

concentration and fluorescence intensity change. Figure 6 shows, 10% in the figure refers to

V1:V3=1:9, and so on.

300 350 400 450 500

100

120

140

160

180

Intensity/(a.u)

Wavelength/(nm)

％

％30

％50

％70

％90

Figure 6. The fluorescence peak intensity of mixed solutions of different concentrations in CH

I and

toluene at 300 nm excitation light.

From Figure 6 show as the volume ratio of solvent increases, the fluorescence intensity gradually

increases. When the volume ratio of CH

I -toluene mixed solution is V1:V3=1:9, the fluorescence

intensity is the strongest, which is almost the volume ratio V1:V3. = 2 times at 9:1.

Study of Absorption and Fluorescence Spectra of Iodomethane Molecules by Solvent Effect

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When the CH

I-toluene mixed solution was irradiated with 300 nm excitation light, the curve

showing the change of the peak intensity of the fluorescence with respect to the volume ratio was

shown in Figure 7.

Figure 7. Fluorescence peak position diagram of mixed solution of different concentrations of CH

and toluene at 300 nm excitation light.

From the above figure, it can be seen that with the increase of the volume ratio of the solvent, the

strongest fluorescence peaks are red-shifted and have a linear relationship.

Under UV excitation, the corresponding fluorescence position of the mixed solution with the

change of the volume fraction of CH

I is shown in Table 1.

4. Discussion and analysis

The relative intensity of the fluorescence from the excitation of the UV light after 320 nm is

relatively weak, it is almost not reflected in the superimposed image, so it is not drawn in this figure.

Because the wavelength corresponding to the maximum absorption intensity is close to the

absorption cutoff wavelength; the electron absorbs the photons and can return to the ground state

without radiation.

Spectrum, found that at a certain wavelength, there is the following mathematical relationship

between the fluorescence peak position λ = λ

· C

+ λ

· C

Table 1. Changes of the position of the strongest fluorescence peak of the

I-toluene mixed solution with concentration and excitation wavelength.

Iodomethane

Volume

fraction/%

280nm 290nm 300nm 310nm 320nm

360

366

369

373

375

363

366

371

375

377

361

366

370

372

373

365

371

373

375

377

364

368

375

377

380

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λ:the fluorescence position of the mixed solution;λ

:the CH

I fluorescence position;λ

:the position

of the ethanol fluorescence;C

:the volume fraction of CH

I; C

:the volume fraction of ethanol in the

mixed solution.

5. Conclusions

In this paper, the UV absorption spectra and fluorescence spectra of CH

I solution were studied, and

the fluorescence spectra of different concentrations of CH

I solution, different volume ratio of mixed

I-ethanol solution and CH

I-toluene solution were compared. Concluded the fluorescence

intensity of the CH

I-toluene solution is the strongest under the excitation light of 300 nm. This

provides adequate preparation for subsequent solvent effects and studies of enhanced stimulated

Raman scattering of CH

Acknowledgment

This work is supported by the“111” Project of China (D17017), the National Natural Science

Foundation of China (21703017, 11604024), the Advance Recearch Project of Weapon and

Equipment (6140414020102), the Developing Project of Science and Technology of Jilin Province

(20180519017JH) , Nanophotonics and Biophotonics Key Laboratory of Jilin Province

(20140622009J)，and the Project of Education Department of Jilin Province (JJKH20170611KJ，

JJKH20181101KJ, and JJKH20181106KJ). Science Foundation for Young Scientists of Changchun

University of science and technology (XQNJJ-2016-14).

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