This document presents a student's experiment to determine the g-factor of a DPPH sample using an ESR spectrometer. The student describes the equipment used, which includes an ESR spectrometer, Helmholtz coil, digital storage oscilloscope, and DPPH sample. The student measures resonance peaks at different frequencies and magnetic field strengths to calculate the g-factor. The g-factors obtained are 2.05 for 12.00 MHz, 2.04 for 14.00 MHz, and 1.96 for 16.00 MHz. The student concludes the experiment was successful in determining the g-factor of DPPH using ESR spectroscopy.

1. Presentation by :-
Priyanka Patel
M. Sc. – Final (Sem.-III)
Roll no.- 223008
Enroll. No.- ECC2264004
1
[Department of Physics]
(2023-24)

2. To determine the g-factor of
DPPH sample using ESR
spectrometer.
2

3.  ESR spectrometer.
 Helmholtz coil.
 D.S.O.
 DPPH sample.
Image:- Condensed Matter Lab, ECC.
Sample Peaks
D.S.O.
ESR
spectrometer
Helmholtz
coil
 Circuit diagram of ESR spectrometer:-

4. ESR (electron spin resonance) also called EPR (electron paramagnetic resonance), is the absorption of an
electromagnetic radiation in the presence of an applied field. It relates the interaction of an external
magnetic field to an electrons’s magnetic field. Since an electron’s spin may either be up or down , so it’s
magnetic moment. That means in the presence of an external magnetic field one state will be higher in
energy than the other. The enrgy of the states is-
where, g – Lande’s g factor
µB – Bohr magneton (0.927*10-20 erg/gauss)
H – external magnetic field.
Energy difference between the two levels is –
And the energyof incident radiation is –
Hence, the resonance condition to be satisfied is-
4
E = ±1/2 gµBH
ΔE = gµBH
ΔE = hν
hν = gµBH

5. Interactions
Sample
 Spin – spin Interaction:- The spin interacts with
neighbouring spin ,energy being constant.
 Spin – Lattice Interaction:- The electron spin interacts
with entire solid ,transforming energy from spin to lattice.
Due to this ,the absorption of RF is possible.
[ωº = eh / 2mc ]
The sample used in the experiment is DPPH , abbrivieted for
diphenylpicryl hydrazyl. It is an organic compound and a
paramagnetic sample with one unpaired electron. It is a free
radical with unpaired electron on nitrogen atom.
The spin of unpairedelctron precesses with larmour frequency
and varies in magnitude. When the Radio frequency falls
in the range of ,the resonance occurs.
5

6. X-plate deflection = 72 mm.
S.No.
Current, IA
(mA)
2Q
I-1
(A-1)
Q
(mm)
1. 131 28 7.63 14
2. 159 24 6.28 12
3. 186 20 5.37 10
4. 215 18 4.65 9
5. 242 15 4.13 7.5
6. 266 14 14 7
y = 1.8425x + 0.1394
6
7
8
9
10
11
12
13
14
15
3 4 5 6 7 8
Q
(mm)
I-1 (A-1)
Frequency = 12.01 MHz
a.) Frequency = 12.00 MHz.
6

7. b.) Frequency = 14.00 MHz.
S.No.
Current, IA
(mA)
2Q
I-1
(A-1)
Q
(mm)
1. 129 33 7.75 16.5
2. 157 29 6.36 14.5
3. 184 23 5.43 11.5
4. 211 20 4.73 10
5. 238 18 4.2 9
6. 264 16 3.78 8
y = 2.2196x - 0.3564
7
8
9
10
11
12
13
14
15
16
17
3 4 5 6 7 8
Q
(mm)
I-1 (A-1)
Frequency = 14.00 MHz
7

8. 8
C.) Frequency = 16.00 MHz.
S.No.
Current, IA
(mA)
2Q
I-1
(A-1)
Q
(mm)
1. 131 38 7.63 19
2. 159 31 6.28 15.5
3. 187 27 5.34 13.5
4. 215 23 4.65 11.5
5. 242 21 4.13 10.5
6. 268 19 3.73 8
y = 2.4257x + 0.4002
9
10
11
12
13
14
15
16
17
18
19
20
3 4 5 6 7 8
Q
(mm)
I-1 (A-1)
Frequency = 16.00 MHz

9. 9
Frequency
=12.00
MHz.
g = 2.05
A. Frequency
= 14.00
MHz.
g = 2.04
B. Frequency
= 16.00
MHz.
g = 1.96
C.

10. 10
 If J results from a combination of an orbital angular momentum
and a spin, then g is given by the Lande’s formula –
g = 1 + [{j(j+1)+s(s+1)-l(l+1)} / 2j(j+1)]
 ESR can be observed at radio frequencies in a magnetic field of few
Gauss or in microwave region of field of a few kilo Gauss.
 Live samples can ‘t be used in ESR spectroscopy.

11. i. Lab user manual.
ii. Elements of Spectroscopy – Gupta, Kumar, Sharma.
iii. Electron paramagnetic resonance in Biochemestry
and Medicine -Rafik Galimzyanovich Saifutdinov,
Lyudmila Ivanovna Larina, Tamara Il’inichna
Vakul’skaya, Mikhail Grigor’evich Voronkov.
iv. Electron Spin Resonance – Charles P. Poole, Jr.
11

12. 12