Vernier VSP-FP Reference Manual

Vernier Flash

Photolysis

Spectrometer

(order code: VSP-FP)

Educational Flash Photolysis Spectrometer

Reference Manual

(version: 12/14/2015)

Table of Contents

 General Information ............................................................................................................................... 4

1.1 Introduction ...................................................................................................................................... 4

1.2 Specifications .................................................................................................................................. 4

1.2.1 Spectrometer Specifications .................................................................................................... 4

1.2.2 Equipment Specifications ......................................................................................................... 6

1.2.3 Detector Specifications ............................................................................................................ 7

2 Safety Information .................................................................................................................................. 8

3 Layout and Basic Principles of Operation ......................................................................................... 10

4 Hardware Description .......................................................................................................................... 12

4.1 Turning the Spectrometer On and Off ........................................................................................... 12

4.2 Optical Filters ................................................................................................................................. 12

4.3 Software Description ..................................................................................................................... 13

4.3.1 Graph Controls ....................................................................................................................... 14

5 The Basic Principles of Chemical Kinetics ....................................................................................... 15

5.1 Stoichiometry ................................................................................................................................. 15

5.2 Reaction Rate ................................................................................................................................ 15

5.3 The Rate Expression and the Rate Constant ................................................................................ 16

5.4 Order of Reaction .......................................................................................................................... 17

5.5 The Experimental Approach .......................................................................................................... 18

5.6 The Relationships Between Rate Constant, Half Life, and Life Time ........................................... 18

5.7 Pseudo Order ................................................................................................................................ 20

6 Data Treatment ..................................................................................................................................... 21

6.1 Data Acquisition............................................................................................................................. 21

6.2 Kinetic Analysis ............................................................................................................................. 23

6.3 The Basics of Photochemistry ....................................................................................................... 25

7 Flash Photolysis Experiments ............................................................................................................ 26

7.1 Base Catalysis of the cis-trans Isomerization of Congo Red ........................................................ 26

7.2

 Isomerization of Mercury Dithizonate ............................................................................................ 31

7.3 Determination of the Activation Energy of the Thermal Back Reaction of One Spiropyran in

Toluene .......................................................................................................................................... 34

 Appendix ............................................................................................................................................... 38

8.1 Spectra of Flash Lamp and White Light LED ................................................................................ 38

8.2 Spectra of Optical Filters ............................................................................................................... 40

List of Figures

Figure 1: Examples of Vernier Flash Photolysis Spectrometer data ........................................................... 5

Figure 2: Detector responsivity vs. wavelength ........................................................................................... 7

Figure 3: Schematic of the Vernier Flash Photolysis Spectrometer .......................................................... 10

Figure 4: Screenshot of Vernier Flash Photolysis Spectrometer Software ................................................ 13

Figure 5: Concentration time profiles of reactant and product ................................................................... 18

Figure 6: Example of a voltage-time waveform after importing into Logger Pro ........................................ 21

Figure 7: Time and voltage (raw data) and absorbance (calculated) ........................................................ 22

Figure 8: Example of a temporal profile of the scattered excitation light. .................................................. 23

Figure 9: Absorption (left) and emission (right) kinetic profilesincluding the scattered excitation light

picked up by the detector ............................................................................................................ 24

Figure 10: Decay portion of the A-time profile ......................................................................................... 24

Figure 11: Congo red, MW=696.67 ............................................................................................................ 26

Figure 12: Ground state absorption spectrum of Congo red (trans conf.) in 20% water in ethanol .......... 27

Figure 13: Kinetic profile of Congo red in 20% water in ethanol ................................................................ 29

Figure 14: Absorption kinetic profile of Congo red in 20% water in ethanol with 2 mM OH- ions .............. 30

Figure 15: Photoinduced isomerization of mercury dithizonate ................................................................. 31

Figure 16: Ground state absorption spectrum of mercury dithizonate (trans conf.) in ethanol .................. 32



Figure 17: Trifluoroacetic acid (TFA); MW = 114.03 .................................................................................. 33

Figure 18: Kinetic profile of mercury dithizonate in ethanol ....................................................................... 33

Figure 19: Structure and photochromic reaction of 6-NO

Figure 20: Ground state absorption spectrum of one spiropyran in toluene .............................................. 36

Figure 21: Transient absorption at 600 nm of one spiropyran in toluene .................................................. 36

Figure 22: Example decay and exponential fit for 55°C measurement ..................................................... 37

Figure 23: Actual data example of ln() as a function of 1000/T ................................................................ 37

Figure 24: Emission spectrum of xenon flash lamp ................................................................................... 38

Figure 25: Emission spectrum of white light LED ...................................................................................... 39

Figure 26: Transmission spectrum of 600 nm bandpass filter ................................................................... 40

-BIPS ............................................................... 34



1 General Information

1.1 Introduction

The Vernier Flash Photolysis Spectrometer is designed to be a simple, user-friendly device for

demonstrating to chemistry students the fundamental principles of chemical kinetics. Every process that

we label as “chemical” occurs as the result of chemical bonds being broken or formed, i.e., nuclei change

their spatial positions with respect to each other. Chemical kinetics is one of the major divisions of

physical chemistry and is basically the quantitative study of the rates and mechanisms of chemical

reactions. Chemical change can be induced in a variety of ways—the one employed in the Vernier Flash

Photolysis Spectrometer is by absorption of light. Thus the instrument serves also as a way of introducing

the student to the concepts and practice of photochemistry.

1.2 Specifications

1.2.1 Spectrometer Specifications

Spectral Coverage

450–750 nm

Spectral Resolution

Determined by an interference filter used. Typically ~10 nm

Temporal Resolution

~100 µs

Time Window

 15 ms

Software

The Vernier Flash Photolysis Spectrometer comes with data-acquisition software necessary to

collect the signal waveform from the photodetector. Subsequent data processing, such as conversion of

the acquired voltage waveform into temporal profile of A and fitting the A profile to an appropriate

function in order to extract the rate constants, can be done by exporting the data into Vernier Logger Pro

software or Microsoft

Excel®.

Data Format

The Vernier Flash Photolysis Spectrometer produces A vs. time data in a form of an ASCII CSV

file that can be easily processed with Logger Pro.

Figure 1: Examples of Vernier Flash Photolysis Spectrometer data processed in Logger Pro

1.2.2 Equipment Specifications

Weight: 10 lbs

Footprint: 8" x 8" (20.3 cm x 20.3 cm)

UL94 rating: V–0

Meets UL796 requirements

Voltage range: 100–120 V & 210–240 V

Frequency range: 50 Hz & 60 Hz

Power rating: 50 W maximum

DC battery: A23 12 V

USB cable: 28 AWG shielded

AC power cable: 18 AWG 300 V

1.2.3 Detector Specifications

All measurements were performed with a 50  load unless stated otherwise.

Detector Silicon PIN Active area 3.6 x 3.6 mm (13 mm2) Wavelength range  350 to 1100 nm Peak wavelength p 970 nm Rise time tr 14 ns Bias voltage VR 10 V Dark current (with 1 M load) ID 0.35 nA Output voltage VOUT 0 to 10 V

Figure 2: Detector responsivity vs. wavelength

2 Safety Information

The Vernier Flash Photolysis Spectrometer is designed and manufactured for kinetic analysis of a

chemical specimen by means of transient absorption spectrometry. It is not sold, nor intended for, nor

should ever be used for any other purpose. The product should be used solely in accordance with the

instructions provided.

 Use a compliant surge protector when exposing equipment to voltage. Failure to do so may result

in damaging the unit.

 Do not use this equipment in or near water.

 Use extreme caution in handling the cuvette when it is filled with liquid. Never fill or refill the

cuvette when it is in the sample holder. Failure to use a cuvette with a dry outer surface or a

cuvette that is leaking liquid can result in the flash housing to malfunction or short.

 This system is designed to work optimally at room temperature or an approximation of room

temperature.

 Do not disassemble the spectrometer case. Doing so may result in damaging the excitation light

source and electric shock.

If the spectrometer does not appear to be functioning properly, do not attempt to repair it yourself.

Please contact Vernier Technical Support for assistance.

Every effort has been made to ensure that the information in this manual is accurate. All

information in this document is subject to change without notice. Ultrafast Systems makes no

representation or warranty, either expressed or implied, with respect to this document. In no event will

Ultrafast Systems be liable for any direct, indirect, special, incidental, or consequential damages resulting

from any defects in this documentation.

If this equipment is used in a manner not specified in this manual, the protection provided by this

equipment may be impaired.

The following are definitions of the Warnings, Cautions, and Notes that are used throughout this

manual to call your attention to important information regarding your safety, the safety and preservation of

your equipment, or an important tip.

WARNING

Situation has the potential to cause bodily harm or

death.

CAUTION

NOTE

Additional information the user or operator should consider.

Situation has the potential to cause damage to

property or equipment.

3 Layout and Basic Principles of

Operation

Xe flash lamp

Detector

LED

L1 L2

photodiode

Sample

Digitizer

Figure 3: Schematic of the Vernier Flash Photolysis Spectrometer

A white light LED is utilized for probing the spectral changes taking place after the sample has

been exposed to an excitation flash. The white light is sent through a sample cuvette via lens L1 and

subsequently delivered to the photodetector diode by passing through an optical interference filter and

objective lens L2. The optical interference filter is used to select the desired wavelength out of the broad

emission spectrum of the LED. While the continuous wave (CW) output from the LED is being monitored

by the photodiode, the photoexcitation flash is sent through the sample. The photo-induced transient

species cause the absorption of the sample to deviate from what it was before the excitation flash. This

results in changes in the intensity of the LED light passing through the sample. These changes are

detected by the monitoring photodiode. The output voltage waveform from the photodiode is collected

and digitized by an internal DAQ device and transferred to the computer for further manipulation.

4 Hardware Description

4.1 Turning the Spectrometer On and Off

 Connect the power cord to the AC input located at the rear of the Vernier Flash Photolysis

Spectrometer.

 Connect the Vernier Flash Photolysis Spectrometer to the computer via a USB cable.

 Wait until Windows

 Start the Vernier Flash Photolysis Spectrometer Software.

NOTE

The 12 V battery that powers the photodiode can be accessed by removing the battery compartment

lid on the side of the housing.

recognizes the new USB device.

4.2 Optical Filters

A 600 nm interference filter is included with the Vernier Flash Photolysis Spectrometer. Insert the

filter into the filter housing that is also included. These filters select the wavelength monitored by the

photodiode. Additional filters can be purchased from any filter company. The size that fits the housing is

12.5 mm (OD), 9.0 mm (ID).

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Vernier VSP-FP Reference Manual

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