Pasco scientific SE-9635 User Manual

Instruction Manual and Experiment Guide for the PASCO scientific Model SE-9634, 9635, and 9636

ESR APPARATUS

012-04273D

10/95

ESR Apparatus 012-04273D

The lightning flash with arrowhead, within an equilateral triangle, is intended to alert the user of the presence of uninsulated “dangerous voltage” within the product’s enclosure that may be of sufficient magnitude to constitute a risk of electric shock to persons.

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

CAUTION: TO PREVENT THE RISK OF ELECTRIC SHOCK, DO NOT REMOVE BACK COVER. NO USER SERVICEABLE PARTS INSIDE. REFER SERVICING TO QUALIFIED SERVICE PERSONNEL.

The exclamation point within an equilateral triangle is intended to alert the user of the presence of important operating and maintenance (servicing) instructions in the literature accompanying the appliance.

012-04273D ESR Apparatus

T able of Contents

Section Page

Introduction .....................................................................................................1

Equipment...................................................................................................... 2-4

Setup with the Complete ESR Equipment..................................................... 5-6

Setup with the ESR Basic Equipment .......................................................... 7-8

Making ESR Measurements ............................................................................9

Appendix ........................................................................................................10

ESR Apparatus 012-04273D

Please—Feel free to duplicate this manual subject to the copyright restrictions below.

The PASCO scientific Model SE-9634, SE-9635, and SE-9636 Complete ESR System manual is copyrighted and all rights reserved. However, permission is granted to non-profit educational institutions for reproduction of any part of this manual providing the reproductions are used only for their laboratories and are not sold for profit. Reproduction under any other circumstances, without the written consent of PASCO scientific, is prohibited.

Limited Warranty

PASCO scientific warrants this product to be free from defects in materials and workmanship for a period of one year from the date of shipment to the customer. PASCO will repair or replace, at its option, any part of the product which is deemed to be defective in material or workmanship. This warranty does not cover damage to the product caused by abuse or improper use. Determination of whether a product failure is the result of a manufacturing defect or improper use by the customer shall be made solely by PASCO scientific. Responsibility for the return of equipment for warranty repair belongs to the customer. Equipment must be properly packed to prevent damage and shipped postage or freight prepaid. (Damage caused by improper packing of the equipment for return shipment will not be covered by the warranty.) Shipping costs for returning the equipment, after repair, will be paid by PASCO scientific.

Equipment Return

Should the product have to be returned to PASCO scientific for any reason, notify PASCO scientific by letter, phone, or fax BEFORE returning the product. Upon notification, the return authorization and shipping instructions will be promptly issued.

NOTE: NO EQUIPMENT WILL BE

ACCEPTED FOR RETURN WITHOUT AN AUTHORIZATION FROM PASCO.

When returning equipment for repair, the units must be packed properly. Carriers will not accept responsibility for damage caused by improper packing. To be certain the unit will not be damaged in shipment, observe the following rules:

➀ The packing carton must be strong enough for the

item shipped.

➁ Make certain there are at least two inches of

packing material between any point on the apparatus and the inside walls of the carton.

➂ Make certain that the packing material cannot shift

in the box or become compressed, allowing the instrument come in contact with the packing carton.

Credits

This manual edited by: Dave Griffith

Address: PASCO scientific

10101 Foothills Blvd. Roseville, CA 95747-7100

Phone: (916) 786-3800 FAX: (916) 786-3292 email: techsupp@pasco.com web: www.pasco.com

012-04273D ESR Apparatus

Introduction

ESR in Theory

The basic setup for electron spin

Test Sample

resonance is shown in Figure 1. A test sample is placed in a uniform magnetic field. The sample is also wrapped within a coil that is connected to an RF oscillator. The smaller magnetic field induced in the coil by the oscillations of the oscillator is at

Oscillator

right angles to the uniform magnetic field.

Consider, for the moment, a single electron within the test

Figure 1 ESR Diagram

Ammeter

sample. The electron has a magnetic dipole

moment (µ

) that is related to its intrinsic

angular momentum, or spin, by the vector equation:

µS=gSµ

where:

=a constant characteristic of the electron, the g-factor

µB=the Bohr magneton =

;(equation 1)

=5.788 x 10

–9

s =the spin of the electron

=Planck's constant = 6.582 x 10

–16

eV-sec.

The magnetic dipole moment of this electron interacts with the uniform magnetic field. Due to its quantum nature, the electron can orient itself in one of only two ways, with energies equal to E0 ± gsµB/2; where E0 is the energy of the electron before the magnetic field was applied. The energy difference between these two possible orientations is equal to gsµBB; where B is the magnitude of the magnetic field.

Resonance occurs when the RF oscillator is tuned to a frequency ν, such that the energy of the irradiated photons, hν, is equal to the difference between the two possible energy states of the electron. Electrons in the lower energy state can then absorb a photon and jump to the higher energy state. This absorption of energy effects the permeability of the test sample, which effects the inductance of the coil and thereby the oscillations of the RF oscillator. The result is an observable change in the current flowing through the oscillator.

The condition for resonance, therefore, is that the energy of the photons emitted by the oscillator match the energy difference between the spin states of the electrons in the test sample. Stated mathematically:

hν=gSµBB

ESR in Practice

For an electron with only two energy states, in a magnetic field of a given magnitude, it would be necessary to set the RF frequency with considerable accuracy in order to observe resonance. In practice, this difficulty is solved by varying the magnitude of the magnetic field about some constant value. With the PASCO ESR Apparatus, this is done by supplying a small AC current, superimposed on a larger DC current, to a pair of Helmholtz coils. The result is a magnetic field that varies sinusoidally about a constant value.

If the RF frequency is such that equation 2 is satisfied at some point between the minimum and maximum values of the sinusoidally varying magnetic field, then resonance will occur twice during each cycle of the field. Resonance is normally observed using a dual trace oscilloscope. The oscilloscope traces, during resonance, appear as in Figure 2. The upper trace is a measure of the current going to the Helmholtz coils, which is proportional to the magnetic field. The lower trace shows the envelope of the voltage across the RF oscillator, which dips sharply each time the magnetic field passes through the

Figure 2 ESR on the

Oscilloscope

resonance point.

ESR in Research

In research, ESR measurements are considerably more complicated than equation 2 would indicate. The electrons and protons in an atom or molecule form a complicated electromagnetic environment, which is affected by the externally applied magnetic field. The various energy splittings and shifts that show up in ESR measurements can therefore provide sensitive information about the internal structure of the atoms and molecules.

The test sample included with the PASCO ESR Apparatus, DPPH*, is a particularly simple substance for ESR measurements. It has an orbital angular momentum of zero, and only one unpaired electron. Therefore, for a given value of the external magnetic field, it has only a single resonant frequency. This makes it possible to investigate some of the basic principles of electron spin resonance, without (or before) getting into the more complex world of ESR analysis.

(* Diphenyl-Picryl-Hydrazyl)

ESR Apparatus 012-04273D

The ESR Equipment

Included Equipment

The ESR Apparatus is available in three separate packages (see Figure 3):

• The ESR Probe Unit (SE-9634) includes:

The Probe Unit with baseThree RF Probes and a DPPH sample in a vial

The Passive Resonant Circuit The Current Measuring Lead for the Probe Unit

• The ESR Basic System (SE-9635) includes:

The ESR Probe Unit (SE-9634) A pair of Helmholtz Coils with bases The ESR Adapter (SE-9637)

• The Complete ESR System (SE-9636) includes:

The ESR Probe Unit (SE-9634) A pair of Helmholtz Coils with bases The Control Unit

RF Probes (3):

13 - 30 MHz

Probe Unit

with base

Additional Equipment Needed:

If you're using the SE-9636 Complete ESR System,

you'll need the following additional equipment:

• a DC ammeter capable of measuring up to 3 A (such as PASCO's SB-9599)

• a dual trace oscilloscope (such as PASCO's SE-9533)

• connecting wires with banana plug connectors

If you're using the SE-9635 Basic ESR System, you'll need the following additional equipment:

• Frequency Meter (to 130 kHz) (such as PASCO's SB-9599 Universal Multimeter)

• SF-9584 Low Voltage AC/DC Power Supply

(or an equivalent supply providing a 10 volt, 3 amp DC output and a 0 - 4 volt, 1 amp AC output)

• Power Supply providing ± 12 VDC

• DC Ammeter (0 - 3 amp) (PASCO Model SB-9599)

Helmholtz Coils

with bases

1000

+12V

–12V

ESR Adapter (SE-9637)—included

in the ESR Basic System, but not in

the Complete ESR System

30 - 75 MHz

75 - 130 MHz

DPPH sample

Current Measuring Lead for

the Probe Unit

ESR Probe Unit (SE-9634)

Passive

Resonant

Circuit

ESR Basic System (SE-9635)

Complete ESR System (SE-9636)

Figure 3 The ESR Apparatus

Control Unit

0 10V

I 3A

max

0…10V–

05V

f/MHz

090°

mod

0…90°

0…5V

+ 12 hidden pages