Infrared spectroscopy of free radicals and transient molecules using a tunable diode laser

201

Journal of Molecular Structure, 60 (1980) 201-204 Q Elsevier Scientific PubhshingCompany,Amsterdam

INFRARED DIODE

SPECTROSCOPY

OF FREE

RADICALS

-Printed inThe Netherlands

AND

TRANSIENT

MOLECULES

USING

A TUNABLE

LASER

P.B.

DAVIES

and D.K.

Department

RUSSELL

of Physical

Cambridge

CB2

LEP,

Chemistry,

University

of Cambridge,

Lensfield

Rd.,

(U.K.)

ABSTRACT

High gas

resolution

phase

spectra flow

using

were

tube

infrared tunable

recorded

after

through

of

transient diode

a single

absorptions b ranches

RQ, also

been

a conventional

pass

species

Lasers

of

the

in

of

theul

thevL

detected

and Yj

band

and

LnErared

have

have

laser

either

sample

fundamental been

tentatively

bands,

assigned.

identified

been

in the 9 and

cell. 2 the chlorineatom at Ll. 3 pm has been assigned to the Ytransition and shows several resolved hyperEine features. from

or

spectra

semiconductor

The

laser

spectrum

Eine

p3/2 The

of NF

components

and

HO2

of

structure

spectra

transient

as CF,( Y,)

the

a discharge-

The 2

other

in

regions.

along

and many

~JO

measured

LL pm

arise

2

in

species

the have

(p3).

INTRODUCTION Infrared lasers

laser

LS now well

coincidence has

spectroscopy

with

Resonance

established

the

laser

(DIR)

(ref.2).

is limited

to spectral

dispensing

with

Laser

sources.

other

transient

free

and

the

Although regions

work

many

Eree

has

radicals

by cw gas

introduced

by

of recent

species carried out with

phase

using

transitions

or electric

technique

covered

is a summary

in the gas

Spectroscople

magnetic

the complications This

radicals

(ref.l).

using

to be more useEu1

proved

of

fields.

have

laser

spectroscopy

of

tting

Magnetic by LJlR it

alternative

effect,

into

Eield

detected An

freque

brought

as Laser

been

lines.

the Zeeman

are

Magnetic

known

become

Eixed

appro

is to use

free

tunab

radicals

and

tunable infrared diode lasers.

EXPERIMENTAL The

spectra

were

equipped with ITorr single

or pass

absorption

recorded

with

a Laser

two diodes centred on 880

less

and

through cell

the spectra

were

the sample.

NF

under

static

2

Analytics and

measured

LO90

cm

after

Inc. -1

LS-3

infrared

. The optimum

the

laser

beam

spectra were recorded with

conditions.

The

other

species

were

spectrometer

pressures had

made

were a

the gas in an L8 cn produced

in a

202 discharge

Elow

for about

1 m. This

et al

and

pumped

a small

by direct

modulating

sensitive than

the calculated

by superimposing

of-1

kHz

of most

of

of

was

current

and

on

could

by impressing employing

were

phase

slightly

hyperfine

of components

beam,

by Menzies

obtained

transitions

etalon

the laser

used

the spectra

to unresolved

spacings

of a Germanium

the pattern

most

diode

the

with

to that

sensitivity

the main

Relative

coaxial

Although

attributable

wrdth,

effects.

on

tube,

is similar

of ClO.

linewidths

Doppler

instrumental

flow

increased

absorption,

The

the

arrangement

spectra

current

detection.

small

along

experimental

(ref. 3) for recording

be detected

and

system

could

larger

structure be measured

the spectrum.

RESULTS a tom

chlorine 3

7

5 structure spacing in the 3p ground state o!i the chlorine -1 atom lies near 882 cm . The diode laser absorption spectra of CL arise from 2 magnetic dipole transitions between the states and their associated hyperfine pJ sublevels Eor which the appropria te selection rules are AJ = f 1, A F = 0, f 1. - -P%

The-P%

Several very

fine

hyperfine

accurate

measured

atomic

by LMR

theoretical

a The

Doppler

(ref.

was

bands,V

Earlrer

that

higher

splittrng

due

several

RQ,

members

oE

hyperfine and

the main

prepared

band

of

has

rotation

branch

F20

result

analysis of

is in satisfactory

for which of

the

other

mode. The change 1 doublet radicals.

these

(Fig.1).

> = - 0.00297

agreement

with

= - 0.00370

spin-rotation tensor

to construct pattern.

linewidths

of N2F4

covered

and

at about

100°C.

by the available by Harmony

Q branches

made,

spacings

at

55 PlHz

were

et al band

not

Two

diodes. (ref.61

of a near

resolved.

The

components

as well

as

the

A complete

assignement

of

and measured

spacings

prolate much

oE individual

yields:

(B' + C' - B" - C")

RQLO the spin-rotation

of they

been

it is possible

of a perpendicular

resolves

structure

the experimental

spectrometer

interaction has

fine

Using

detail.

drssociation the region

laser

the

41,

rules

with

in the spectra.

to experimental

the promrnent

(8' f C' - B" - C" This

selection

the appearance

components

the RQlo(N)

in

resolved

(ref.

of hyperfine

infrared

of

37 Cl are

agreement

thermal

fall

the drode

to spin

branch

the above

contribution

by

y

and

splittrngs

resotiuion

components

resolution

35Cl

in excellent

and

theYI

individual

top.

1s

Erom

1 3' in a conventional

work

showed

51,

the complete

radical

inErared

beam

spectrum

width

this masks

The

components

changes is about

splittings from Eaa the order

cm-l that Eor the analogous molecule -1 (ref. 7). A preliminary

cm

shows

that

the principle

= - 952 MHz

to - 900 MHz

of magnitude

expected

component on excitation

by analogy

with

203

0.025cm-1

1231

(24) 1. Three

components

spin-rotation

doublets.

Fig.

band

The Yj extensive which

absorption

we

in which

has

band

theul

to be more

cm

-1

to CF 2 (0,).

in CF2CFCl

the new

1220

useful

cm

-1

Features

at

, by analogy

For an

initial

theyl

band

OF NF2

(ref.

8). We

have

oE a microwave

Part

is known

of

region

the products

for assigning

no distinct at

in

1100

branch

was used in the discharge

discharge

band

in the

assign

evidence CF2CFCl

microwave

Lies

the RQIO(N)

spectrum

tentatively

Supporting

V3

of CF2

of

(221

of

spectrum

to produce

to be a strong

the resolution with

oE CF2

the diode

the corresponding

4 in figure

spectra.

A

9). The

(reE.

laser

mode

spectrometer;

in NF2,

promises

analysis.

H02 The

vibration-rotation

states shows

oE H02, that

observed coil

and

the new

oE

a multiple

pass

the

allowed

spectrum

results

ceLL

are

the ground

transitions

in flowing

technique.

OF

and

vibrationally

the 9.1 pm LMR spectrum

of a transient

is struck

preliminary

sensitivity

values

from

are many

transitions

the radical

These

calculated

there

discharge

term

using

is

lLO0 -1 1106 cm present

species

near

Pixtures.

tentatively

Experiments

This

assigned

absorption in which

path the

excited

the radical, -1 cm region.

the

H202/ke

short

in progress.

in

of

(reE. We

when

is a known

(tij) 1:

have

a Tesla

source

of

to H02.

lengths laser

show

radiation

2.

experiments

the same

source

of

from

an

in CF

is shown

comes

to CF2

source

detected

discharge

the spectrum

resolved

showing

the inherent traverses

204

0,l c m-’ I

Fig.

2. Spectrum

attributed

to CF2

at

I

1105

cm

-L

.

REFERESCES 1 J I< C. Johns, A R W PlcKellar and M. Riggin, J. Chem. Phys., 68 (1978) 3957. Davies and K PI Evenson, 2 P.B in 'Laser Spectroscopy' Vol. 43, Lecture Notes in Physics, 1975, p 132, Springer-Verlag, Berlin. Toth, Applied Optics, 16 3 R T Ilenzles. J.S Elargolis, E D. Hinkley and R.A (1977) 523. 4 V. Jaccarino and J.G. King, Phys. Rev., 83 (1951) 471 and 84 (1951) 852. 5 PI. Dagenais, J W.C. Johns and A.R.W. ElcKeLlar, Canad.J.Phys. 54 (1976) 1438. 6 M.D. Harmony, R J Schoen, D R. Lide and D E. blann, J. Chem. Phys. Elyers, L J 35 (L9hl) 1129. 7 F.J. Lovas, J. Phys. Chem. Ref. Data, 7 (1978) 1445. 8 A S Lefolln and G.C. Pimentel, J. Chem. Phys., 55 (1971) 1213. 9 W H. KirchhoEE, D R. Lide and F.X. Powell, J. Elol. Spec. 47 (1973) 49L.