Infrared and Raman spectroscopy at high pressures

101

JourmlofbfoleculorStmcture,113(1984)l01-116 Eb-svler

Science

INFRARED

AND

W F

DR

B V

F’ubhsbers

RAMAN

. Amsterdam

-

Prmted

SPECTROSCOPY

AT

m The Netherlands

HIGH

PRESSURES

SHERMAN

Department

of

Physics

King’s

College

London

Strand

London

WC2R

2LS

(U-I;.)

ABSTRACT Pressure IS accepted theoretically as a useful variable However tn studtas on liquid or soltd samples It IS stlii reiatlvaiy unusual for pressure to be used as aa experimental vartable The reluctance of experrmentaltsts to use thts theoretically attractive varrable IS caused matniy by the technrcai difftcuitres assocrated with the use of sufficiently high pressures In thls talk I WIII try to show tnat m many cases the exparrmental lrmrtations are no longer those introduced by the use of high pressures Hlgh pressure spectroscoprc studies clearly imply the use of htgh pressure spectroscopic cells A brief account WIII therefore be given of the varrous types of high pressure optrcal cells which are currently betng used for spectroscopic studles Each fndivtduai high pressure spectroscopfc study has its own special justificatron However there are a few quote general observattons that can be made which cover many of the specrfic objectives of rndividuai high pressure spectroscopic studies For example frequency shifts carry unambiguous rnformahon about (I) pressure Induced anharmonic terms in the relevant potential fuficilofl Ci e the potefltlal V IS a functron of drstance d. therefore prsssure can be used to change d and study V 1 (III ail known materials undergo structural phase transitions If the form which Is thermodynamically stable under ambrent conditions IS compresssed to high enough pressuras. thase high pressure phases should be studied (III) as the application of pressure forces a material towards a phase transrtlon. the spactroscoplc study can be used to gal” tnformatron about the approaching structural instabliity. (iv) vlrtuaiiy all infrared and Raman spectra contarn examples of Fermt resonance which confuse tne lnterpretatron of the spectra and the effects of pressure are valuable alds to the correct assignment of the resonattng levels (VI pressure Induced frequency shifts can often grve extra InformatIon to help with the more reliable assignment of features within a spectrum The above points will be discussed and illustrated by examples chosen mainly from recent work by members of the spectroscopy group at King s Collage London lNTRODUCTl0.N Much of

of

producing

which

for

Thts

Is

example

fig

amblent-(effectively along

a

Ilne.

OOgP-2860/8-I/803

research

(such

produced

as at

thermodynamically

conditions (see

be

in

Interest

materials

cannot

become

the

7)

drawn Ambtent

zero)-pressure the

temperature

00

0

1981

high

diamond.

amblant

stable

usually

at

pressures

cubic

boron

pressure

under out

More

different on

a

EBerler

Sctence

nitride

are

a

dot

that

Is

Publtshers

on

-

and

B V

posstbility ate

different

phases

pressure phase

such

a

experiments scientiftcally

the

polyethylene

temperature-pressure

conditions

Much

from

generally

temperature

variable-temperature axls

comes

diagram.

diagram are

interestrng

and

located can

be

1

102 Studied

at

Interest

that

must that

region

dot. be

Is

There

waiting

also

Fermi-resonance the

work

that

oressure

has

no

an

as

are

available

The

use

of

pressure

tn

hlgh

spectroscopy

the

all

analytlcal

variable.

purooses

reflec*ts

the

ot!ier

of

that

to

work

necessarily

llmlted

by

high

thareforo

briefly

avallable thap

-__

I

more

lkbar

=

kilobar.

In

lO*Nm-2

in

of

the

high of

a

changes

about

ln

the

the

(1

variable

for

high

extra

varlable

tha

e

use

of

temperature

when

use

at

useful

research

that

are

avallable

spectroscopy

so

far

of

by

high

the

taken I

cells

required (1 8

(ii)

1

the

under

describe

ThiS

use

of

high

use

wlth

the

has

is

most

our

for

other

will

come

This

own

the

useful

paper

group

be

found

simply than

for

that

deny

that

widely

cell

the

sectlon

many

not

be IS not

now more

-

not of

consldered

purity.

etc

very the

often

sample

stability.

still

interesting

been

will

pressure

It IS

some

be

I

llmltation

results

is

Since

experlment is

temperature

will

that

high

results

apparatus

been

used

lnevltably

point

the

spectroscopic

lollawing

almost

particular

spectroscoprc all

was

Instrumental

that a

usually

that

One

spectroscopic

accuracy.

has

cell

this

__-_ IS the 1 GPa

thls

It has

that

required

range 10

mainly

reported

optical

equipment

spectroscopic

not

the Thus

IS a

London

of

rerearch

limit

the

work

been

presscre

pressure

In

performed

Col!ege

into

projects

pressure

thrOughoUt

King’s

It will

which

work

at

paper.

that

high

falls

tield

pressure

pressure IS

will

reported

research

that

from

that

spectrometer

pressure

pressure

available

h&h

factors

high

contention

pressure

the

beyond of

0

a

pressures

to

high

as

pressure

hlgh

now.

The

=

as

and

spectroscopy

forms

in

this

Olten.

kbar.

of

Idbordtories

famlllar

-___--__-_The

use

group

lhls

kbar’

aspec:s

comparable

that

active

resolution.

However.

greater

am

been

other

pressure

vlbratlon.

Informative

high

be

examples

capablllty

those

to

throughout

llmlted

spectroscopic

currently

the

limito

significance

automatlcally

I will

has

very

of

the

spectroscopy

true

has

The

part

are

the

emphaslse

equipment

been

performance

towards

be

In

pressure

supoort

pressure

the

this

1

USinQ

pressure

work

spectroscopy

that

SClentlflC

pressure-temperature

of

of

materials

had

the

the

fact

high

by

directed

L

of

of

groups

The

to have

Most work

the

trying

I have

Is of

I

high

It has

that

now

only

can

abova

spectroscopy of

for

types

avatlablllty

SpectrosCoplc

study

the

category

examples

most

most

condltlons

second

interest

that

condltlons

the

the

anolytlcal

pressure

in

Virtually

limited

to

certain

pressure

both

for

InCreaSIng

reasons

for

ambient

cover

cass

the

more

avallable

analytical

of

under

direct

aid

within

values

function

IS to The

that

of

a

intention

pressures

simple

much

However.

line

studled

du/dP

material


be

some

as

of

The

from

to

that

experlmentally

Characteristic

Spectrum

in

along

becomlng

are

variable

or

common

and

equipment

IS for phenomena

pressures which

-used

unit

in

high

pressure

research

work

103 occur

at

generally

pressures

below

accepted

for

vibratianai with

spectroscopy

pressure

smaller

than

at

rates

of

for

some

pressura

mduc_ad

frequency

defrne

qurltt

pressure.

measured

kbar

are

groups

are

and

ii

that

HIGH

the

be

most

of

be

10

the

pressure’

a

can

kodr

often

srgn

wlli

been

for

frequencies

1 kbar

the

has

defmttton

be

ten

IS close

of

most

normally

~nrt!al

rale

of

change

made

up

to

1700

shift ilmes

to

the

pressure

be

enough

of

to

frequency

with

be

of

use

of

about

in

to

thus

the

large

range

up

vIbratIona

one

or

other

relatively

to

20

those

7 Mbar) above

number

of

200

research

kbar

spectroscopy

of

short

(1

earlrer

trefs

1 and

articles

for

the

paper

EQUIPMENT

different

I will (or

tn

kbar

measurements

lncreastngly

pressure

refer

30

literature

an

pressures

high

to

However.

scale

whereas

Included

hydrostatic

been

hrgh

pressure

consfder

the

quasi-hydrostatlc)

spectroscopic

four

followlng

spectroscoprc

systems

categories systems

have

only

but

be

will

found

included Fluid

(I)

Solid

f IV) A

high

3)

Ii. 1 HIGH

Fig

and

its

pressure

generation

piston-m-cylinder

cell

spectroscopic the

scope cell

of

IS a

sample

general must

type

(DAG)

to

high-pressure

be

briefly

systems thus

htgh be

present pressure

monltored

have

been

enclosure by

constraints

also

paper with

at

least

electromagnetic

cannot

be

discussed

here

mentioned

WINDOWS

the

surrounds viewing

internal

the

enclosed

the

wlndow

P

with of

spectroscopic

window

1 shows

generatlon

outslde

the

PRESSURE

spectroscopic

wtndow

are

allow

the

pressure

anvil

pressure

Although

ref

external

untaxiai-pressure

these

to

radlation

sUppGrled

of

with

cells cells

diamond

but

A

pressure

medta

number

window

cells

media

The

descrlbsd


media

Ltquid

f II) (III)

one

day

of

SPECTROSCOPIC

the

the

but Thus

daflne

of

have

reviewed

necessary

Descripttons

to

pre&ure

‘hrgh as

Vibrattonai

spectrum

fluorescence

regular

cannot

In

pressure

1 cm-l/kbar

a

of

convement

unambiguously

unusual

recently

PRESSURE

appeared

of

magnrlude

ruby

makmg

it will

details

high

in

measurements

somewhat

I have 2)

the

deftnttron

o

on

still

order

A

dccurdtaly

(du/dP)

under

to

kbar

it IS quite

bands

requrred

Speclroscoplc as

the

shlfls

P,l

time

studied

thus

mmimum

The

this

some

area

seatmg

three In the of

most (a)

:he

nrndow the

exceeds

commonly Poulter and

window the

used window

forces ensures

contatned

types is

shown

It against that

the

pressure

of

Its

high

where support

pressure CP)

pressure

as

the The

(PSI grven

contained un-

between by

the

the

104 standard

‘unsupportsd

Fig where

the

lo

to

area’

shows

pressure

The

por Is low

l(b)

uuler

outer

PS

window

medfum

IS dropped

Ihe

the

expresston

Drtckamer

lrdnsmtttrng

p’ussure

frdcturu

support

the

PD2/(D2-d2)

(usually

OILon

along

dn

partrcularly

1s used N&I)

progresstvsiy

surfdoe

surface,

=

which

In

also lhe

hlls

wtndow

wtndow.

0~1~

soltd

If non -amblont

msdla

the

narrow

ports

say

Ol

cells window

until

I: is

too

Is

used

sapphtre

tomperaturos

are

to

be

used Fig gasket

l(c)

so

Thts

fluid other

shows to

as Is

types

tne

generate

shown

of

cell

rn

opposed

force

a

higher

pressure

DAC

configuration.

the

window. in

where the

the

gasket

but

window

than

it has

Is

in

been

iorced

the

used

onto

a

enclosed successfully

In

also.

ta) Flg

1

Three forms of high pressure spectroscoptc windows (a) Poulter. (bl Drtckamer Cc) Opposed force (DAC) marked W the axts of the lrght path IS marked L. and pressure P Four

strength

types

may

of

limit

experimental the

maxtmum

may

ltmtt

the

spectroscopm

may

limit

the

radlatlon

become

unusuably

scramble

Constderatlons spectroscopic has

posstble

refs us

I

to

found

S.

burst

t

IS the

are

For

(ref at

should

4)

glass given

thickness

can

be may

that

the

It

a

D

IS

of

by the

may

P

=

diameler

(1)

Its

ratio

be

Ita

absorptton (1111

such

compromlse

a

standpoint apprecrated

corractly

size

may

as

to

glass 64

(t/D1 01 the

and a

between large the

how

shaped

wtndow-burstrng float

Its

signal-to-noise

tnevitable

over

from

approximately and

(II)

collected

IS

radiatlon

generally

set

cut

be

window

Spectroscopically

mounted

recent

wmdows

the

the

the

attained

high-pressure

not

IS

properly in

a

by

propertres

by

requirements from

Imposed

data

point

represent

used

are

example. that

pressures

wtndcw

(III)

be

the

carrleo

whereas

they

which

11s blrefrrngence

high-pressure

when

6)

and

advantage;

window

materials

( iv)

Information

(i)

and

stQntficart

to

be

that

ovar

throughput

small.

may

pressure

range

polarlzatio-t

ihe

lrmttatlon

The wlndow the rstatnsd

tests

strong

where

wrndow

supports. up

prsssurrzsd

unsupported

window smallsst

P

to

(see 20

kbar.

wlth

Octoll

IS in

kbar.

area

That

105 expresston

should

windows

have

45

(ref

kbar The

to

ail

is

to

significant

not

laser

beam

radiatron

can

collected

through

3

II

HIGH

2

A

and

wade

four

gas

compressor

Clearly

cell

IS

Itself

requires Cells

the with

too

identical

many

have

of

the

windows

but

up

to

glass

at

least

I

other

support

gases

of

and

that

can

be

applred

the up

liquids)

agaln

in

about

be

taken we

thts

way

20

than

simple

mlxlng

of

In

refs

I and

traced

in

indrcate

kbar

has

a

srgnal

the

some

3

the

d&all.

with

many

literature

slngie

IS

by

to

be

piped

over

example

any

from

sets

the

from

‘fluid

such

at

an of

77

K

external

the

a

maraglng

specific

ceil steel)

The but

It

experimental

cell

conflict

too

between

Commercially present

the

system

tne

requirements kbar

of

primarily

one

into

from

weaken

posslbie

lt

removing

made

for

ceil used

into

generatlng

made

a

window been

pumped

could (It

not see

two

it

pressure

could be

be

mounted

construct

hrgh-pressure to

more

IO

are

exte:nal

must

Here

wlndows

used

an

m

can

type

about

(or to

Raman

7)

descrrbed

a

srze

to

geometries care

no

samples

simple

convergmg without

dlverg,ng

effects

of

less

surfaces

slowly

window

a

these

are

window a

are

edge

earlier

actual

Solid

the

pressurrzed

studied

that

generatlon’ up

They

Thus

conslderable

rref

are

do

lrsted

half

relatively

ba

have

they the

CELLS

cells

can

a

clear

lsotroprc

once

wmdow

Whereas

suffer

Whaiiey

development

pressures

can

and

different

pressure

that

can

We

lkawa

the

angle

of

even

near

through

other

centre

because variatrons

pronounced of

~111 be

strain-Induced

Is

more

middle

some

SPECTRCSCOPIC

about

but

spectroscopic

tested

index

scramblrng

wlndow

catagorles

different

requirements

kbara.

and

ana/or

perpendicularly

the

system

windows

passes

the

through

of

axternal

heitum

20

5)

This

much

In

components

at

shows

are

porartzatron

Here

the

are

passed

hrstorrcal

of

they

range natural

refractive

at

the

years

medium

of

llmlt

tref

self-evident

through

an

range

to 30

2

be

as

past

each

wllh

4)

so

which

PRESSURE

references

kbar

the

passes

slgniflcant

poiarlzed

rrefs

experlmental

25

transmission r Iv)

effects

than

which

any

dlffarentiy

to

strain-induced The

area

light

the

(II)

necessarily

pressure

suffering

Fig

of

develop

for

for

our

up

However

unsupported

than

beyond used

6)

materrais

subjected

used

been

significance

brrefrrngence

the

be

spectroscopists

wrndow

the

not

certainly

upper

much

by

available limit

rnciudlng

the

to

the

tubing pressure

106

Fig

2 a

Tno-wmdow

high

pressure

opbcal

cell

0b

Frg.

2(o)

Cell

mounted

vltnin

cooling

jacket

107 A hlgh

pressure

Raman

HIGH

hand

pressure

p&ton

It friction double (A2/AT)

of cell

quoted

Into the

range

used

up to perhaps

short

fatigue

of

the higher

set by the hlgh-pressure piston.

pressures

piston

up to perhaps

4)

Thts

IS required

drives

the

to supply

small

area

within

which

the sample

to rest

when

the

I e

when

grves

the

for

or

ultimately Wlth

the

careful

50 kbar

long

windows

should

= P2A2

pressure

IImitation

multiple

a fairly

The

PTA1

of

working

could

design.

Pt

lrmrtatlon

the = Here

on

cylrnder

life.

or

IS

higher

if a

carblde

the 45

be

to

probably

a tungsten
this

could

smaller.

lrmlt woulo

usrng

be possible

on

or

15 or 20 kbar

be made

pressure

IS mounted

factor

component

a

hlgh-

net force

lntenslfmation

The

a pressure

be tolerated and

WITH

comes

autofrettaged

pressures

(ref

IS possible

Usually

twice that figure

In fig 3

cylinder zero

geometries

USE

assembly

ram

of the areas

a properly

life could

gauge

area

piston

obvtous

FOR

type cell

pressure

becomes

the ratio

IS less

However

withstand

the

IS shown

tbar

liquid-filled

then

Thus

again _ a wide type

and

type

CELL

lntensifler

arrangement

Pp

I4

to the large

is Ignored

piston

TO

3

pump

low pressure

intenstfler

RAMAN

MEDIA

Fig A small

of the

PRESSURE

LIQUID

known

cell

kbar

be

106 window

testing

Fig used

system

4 shows

by cur

Infrared

transmission 77

tusualiy

NaGI)

K and

into the cylinder

jacket

which

lntenslfier

difference

hydrostatic medium

the central

the

part

the use peak

of the cell

but with a short

hbar.

(50

transmrtting

seen

kbar)

steel

life of perhaps

halide

carbide

piston

its outer-

cell

which 9)

whrch

pressure

The

a non-

solid

avolds

matsrrai

the

Note

operates

cycles.

an

The

applies

which

wrndow

cyirnder

20

alkail

to contain

to a br:ttle

for

to be essentially

tref

that

up to 50

after

whrch

It IS

replaced A diamond shaped. surface IS a

anvtl cell

bounded of the

!iuId

However a sample.

tor

for

small

hale

that

*soft scircl’)

a

hard

which

(DAC)

by the hrgh

solids

(or

IS smaller

IS shown

pressure

end

IS drilled

I”

it can when than

@

occupy

frg 5

in

the

cwntrw

the whole

hydrostattclty the

sample

of

the

high

4

Drickamer

with a fluid

medium

cell

fief

6).

IS drsc inside

If the

sample

volume

pressure

CARBIDE

type solid

the

it IS usual

ALL OTHER PART9 KE 6% STEEL Fig

volume and

gasket

pressure

IS importart)

hole.

gasket

NNCSTEF!

The

fiats of the dramonds

1

been

at temperatures

an

within

medium.

caster

has

primarily

the tungsten

mounted

type windows

IS a supported

working

Is

way i3 that of the fig.3

but IS much

of Drickamer

pressures

When

it IS clearly

m a simriar

to the sample.

allows

to bpply

ram

medium

of this type

which

up to 50 kbar

by forcing

halide.

1s the soled pressure

pressure

also

a low pressure operating

range

cell

cell

it Is intended

transmitting

Is generated

with alkali

type

years

pressure

pressure

pr-sssure

a one-window

of a Drrckamer

10’ many

in the The

filled

contains

type cell.

prmcipai

need

K

Is effectively

part

(ref.81

spectra the

which

6)

pressure

group

600

and

ref

hlgh

research

between down

of

the

to surround transmitter

109

Fig The

Inevitable

requirement that

must

end

fiats

of

The of

the

that

in

no th3

end

successfully large

In

of

high

present A

day

VIS

UV

conductlvlty scatterlng the of the

transitions

X-ray

diffraction

e xperiments the

experiments

extrameiy

small

could

performed volume

Clearly

the this

and

exampls

high

end

work

up

to

70

work

up

to

400

kbar.

IS less

aperture smaller

than

fiats

pressure

for

much

1s very

small

(usually

studies Many

spectroscopic

pressure

for

window is

the

high

but

kbar than

the

half

apertures

windows

volume

space

used

10)

other and

types

DAC

certainly

s

the

the

with of

DAC

IS be:ng

interferometers) experiment

are

probably

most

widely

and

are

quite

also

We

most

used

type

popular of

system

research a

commercfally

heatlng

avallable

melting.

reactlon

growing ba

wlthin that

Mossbauer klnetlcs.

ruby

performed DAC’s

IS available

DAC

fluorescence.

compresslbllity

crystal

that

recommended

spectroscopic

for

VlSCOSlty

solublllty

For

tref and

smaller

required

typlcaiiy

ceil

Plermarlni design

the

are

studies

phase

of

are

sample

advertisement

cryogemc

are

lnrrared

pressure

terms

mm

sample

optical

high

recent

tiny

and

high-pressure

in

IS effectively

for

some

Block

mm

dlametQr

Raman

that

pressure

ObseNatlon NIR

of

4

which

used

for

wlthln

0

avaliabie

used

number

performed type

the

the

DAC

1 2

than

flat

conventionally

a

after

pressures

about

gasket

diamond

are

ior

If higher

more

ceil.

between

seen

diameter

Although

a

be

used

of

hole

anvli

compromlse can

Se

d&meters

Diamond

5

in

the

have

and

under

NMR

been

truly

high

Brlllouin as

some

within

in such

of Some

pressure

remarkable

working

Raman.

electrical

measurements’

cell

However

I R effect

dlfiuslon

pressure

‘visual

i&ted

v’ew a

of small

volume

doss

pose

procedure the

two

fiats

another wifh

high

must

up

a

cell

this

does

sourcQs.

require quite

capable

Ill

are

not

The

the

dnd

small

The

Informdtlun

oven

with

pressure

levals

that

intensity changing

the

by

the

The

(le

2)

d

a

laterally

remarn

parallel

to

a

design

the the

most

hrghQ*#t

anvils

delay to

in

In

3

rn

the

available

or

to

form

of

4

r They

do

(by

not

the

yet

relahvely

Unfortunately that

It

broken

they

use

way

high

from

However be

srnce

rodtme

figs

even

pressures

not

dellvery

rmagfne

those

popular

versatrle

are

but

prOCQdUr9

avaliabie

stahc

surprrsrngiy

up

and

one

problem

settlng

commercially

the

trrvlai

such

DAC

s

are

-measured shapes

a

here

‘normal’ v2

to

Lntensltles

consrder

band

might

dnd

spectroscoprcaily

and

be

changes

in

of

these

Y

but

the

7 and

gives

may

of

bands

wlthln

‘expected’ 2)

prove

to

abnormal

rt can

linearly

very

a

variattons

However

roughly

only

well

funchon

Y approxrmdtely

ChdngtQ

it IS the

a

various

change

this

should

changes

band.

to

the

detail

refs

eXpQCted

~ntensilies

‘normal’

In

(See

as

of

with hnear

slowly

wrth

with

contarn

useful

behavrour

that

Is

rnterestmg most

hydrogen

frequencies

---

intensihes

are

insensihve

but a

slowly

X-H

witn

pressure

dt

rise

bonded

resonating

sometimes

a

oressure.

show

bands

spectrum

as

approximately

frequencres

to

can Most

a

pressure

(and

stretching

one-another

rs changed

glvsn

literature

now as

a

It was

possible

monatomlc

soilds.

examples only

is

a

allgned

durrng

DAC

nut

will

structural

but

very

shift

cr

two

raptd

slowly

change

Ilnearly)

usually

involving In

relative

continuously

abruptly

chemical

bands

changes and

with

decrease

with

and

change

is

induced

pressure

spQctroscoplcally and

for

pressure.

discontinuously

be

as

percentage

Most

are

as

to

easier

such

are

magrutudtls

more

but

the

Is

is

carefully

and

this

diamond

may

space

sh._fpus

example.

pressure.

if the

commercially

general

bdnd

prsssure

For

of

ingenurty.

It is

cells

for

(for

scientifically

1

IS not

in

:he

up

which

that

pressure.

that

up

littie

there

another

required

DAC

very

self-contarned.

working a

frequencies.

p’rameters

shown

fact

the

be

STUDIES

There

these

PI

of

parameters are

spectrum.

be

and

present

EXPERIMENTAL

pressure

of

at

of

Items’

operators)

one

is

up

must

Scme

care

the

setting

‘stock

to

small.

with

expensive.

unskliled

great

settrng

flats

pressures

alter

and,

and

Qnd

parallel

it Is

careful

be

to

cells

not

equipment

several

seem

made

wall-deslgnad

currantlyavaiiable

are

be

highest

All

to

problems

pressure

the

pressure

doQS

special

The

from

most

contains function to AS

examples of

systematically type

categories

of

pressure

crystals. Here

most In

the

consider

is

of

longer

the

dlatcmlc there

types

material review

different

molecular

space

for

studied articles

types

of

crystals one

or

two

(rafs

I

materlal. 1 givlflg key

examples

111

b

’

0

I

2

3

4

5

PRESSURE/K

Fig

6

Frequency

Fig

6

In

the

far

I”

regions

shows

like

can

quite

precisely

type

be

0r

In

this

A

the

of

molecule

the

VII+VIII

which

slrongly

flrsl

VIII

looklny

curve exlend

examples show

that

0

pressure

(refs

of

as

mode

lncludad

energy are

RhBr

to

is

good

to

change

phdse

11

(I)

high

define

(NaCI

even

pressure

Cdu/dP),

II-I frequency

lrdnsltion

12)

measured

emphaslse

low.

enough

dlscontlnuous

lanes

to

about tho

15) 190

phase

2.04*

beyond

be

looklng fig

kbdr

trtple

at

the

phase

wlthln

Into point

of

In

10

type

that to

to

1s

CsCl

vlctnlty study

the

tceVl

region

for

pressure VI+VII

III*IX

ax!s

which

and

show

the

but be

recent

that

mentioned

of

ice

VII

161

have

et

that

al

(ref

VI-VI the

triple

approached

curve from

which Klug

and

ice

been

point.

Ilquld-Ice

IceVl-hqurd

work

stud!es

be

liqutd

the

other

01 the

of

should

Plermdrlnl

showed

spectra

aspocls

spectrum

H20

Infrared

then

the

Raman

two

Figures

of

latter

the

axis the

and

In IS

transltlons.

V-VI.

various

Ihe

diagram dtagram

order-dl=order parallel

diagram

could

phase

studying

This.

which

phase

This

Illuslrdle

three

DAC.

the

complex

1~111. Ill+V

studying a

(a)

been

and

those

been

GPa)

extendsd the

7

hdve

diagram

02

9.9

7

temperature

14)

13

a

fig

virtually

10 the

figures

before

(ref

could

dnd

It shows

c,langes.

(refs

forms

has see

transmon

recently

at

T

kbar

order

slructural

hdvo ILL

(69*2OC.

ftrsl

IS H20.

parallel

lo

5

never-the-less

kbar

virtually

Whalley up

strongly

25

order

slgnlllcance

dnd

or

of

been

available

4

function

the

has

(1113 the

bands

lines

Howover have

the

even

as

on

This

where

that

below

(b)

Wo

RbBr

pressurs

12)

(II)

d

of

7

case)

and

dlrforont

of

and

out many

for

lrdnsitlon

mode

I R

for

range

lnlerestlng

far

errec:

small

pressure

0

effect

11

carried

iho

T

the

(refs

I R

work

typlLdI

of

6

BnR

that

VII

melting

would

not

dlrectlon

ll.2

Fig

7

Phase

diagram

of

Ice

I 0.oall 148 K cm-1

GPa

4

0.27 -a 165 K 3 cm-1

o-29

246 K 3 cn-1

0.28 150 3.5

GPa

CPa K ca-1

0.44 Gla 148 K 4 an-1

I

1

333x>3loo

0

ivcD.f-’ Fig

8

Raman

speclra

of

ices

I. II. III. IX.V.VI

and

VW

113 Fig

9

shows

I. II. 111 IX. V VI between for the a

the

the ice

tranlahonat

13)

spectra

various has

very

the

Cref

for

and

way

promrnent

phase O-H

of

diagram

mode whereas the

the

transtttons the

Thts

At

O-H--

0

mode

longer

O-H--

frequencies

Flg

9

of

distances Increases 0 In

Ice

In

any

but

Frequencies lunchon of

terms.

In

long one

9

tref

a

shown

O-H stretch and pressure passtng

ICE,

spsctra

whtch

Raman

0 O-H

the the that

wrth

Within

phase

varrous

the

stretchmg

pressure

effecrts

the

scan by

of

relationshtp dlsttncttve

that

vary

13)

denser

O-H--

It IS clear

O-H

tncreasrng

phase

relatively as

the

These

bonds

favours

that

fig

top

spectra

unambrguously polnt

frequencras

with In

Raman

completely

show

general

the

order-drsordsr

phase

spectra

offer

dtagrams

way

decreases

distances these

the

mode In

transItton

hydrogen

that

the

latttce

of

the

otherwtse

phase

decreases

a

th-

spsctra

tllustrates out

region

Ncrtce

and

tllustrated

IS

mode

17)

Raman

compare

mode

the

show

lattme

to

lattme

strengths

thts

frequency

Increases

III

mapprng

translatronal

stretching

trnf

These

adopted

reltable

latttce

VIII

IX and

phases

It IS intereshng most

and

be

distances frequency

promrnent through

I must

increases

In

terms

reduces

decreases soas

reverse be

the

phase

pressure

and to

In

to

be

translatronal lattrce vartous phases

the

produce

steps

expected

the thts

lattice

stretch

The

changes

disconttnuous

phase the

drscussed

As

and

across

one

O-H

structures

structure

Ice

any

whereas

the

can

frequency pressure

mode

the a

IS a

of

114 relatively

unstable

G-H---

short support

0

hlgh

structure

with

pressures

respect

Even

dletancee. as

at

shown

by

our

to

nottce

the Thts Ice

10

spectra

shows

an

are(l)

transthon second

just

We systems small

Ice

I-IX

The rrght

hdd

a

Infrared of

bands

lempernture)

dre

very

usually

unamb

quote

stable

at

because polnhng phase

long-term and whrch

guous

mleresl

Aamdn at As

cusp

I”

the

speclrd

of

low the

S.peCl’d

the

to

these

drH

The

two

IS no

pornh

and be I.

seems

(II) I-II Ice

III

to

temperatures

alkalr

halrde/rmpurrty

contarn

somohmos cledr.

main

me

dragram

lowest

systems

IX

It should

there

of

(and MI

I and

temperature

phase

tho

speclra

tomporatures

low

ices

suggests that

In

dragram

of

at

dragram

tt suggests

dawn

18)

b&

K study

88

pressures

phdse

the

not

3

pressures

recent

high

of

will

km-‘)

various

this

the

the

Cref

1

Shift

downward

sharp

K studles.

250

K and

although

because

strucxture

D20

from

IS rnloreshng

pomtl

The number

88

Example

open.

have

at

I IS not

1s from pornt

II trrple

rematn

88

150

Raman

pressure thls

I

Reman

Ftg

recent

I

50

10

increasing

temperattres

bar

1 1

Fig

to

low

the

a oven

Ion

relatrvely at

rnturpretat!on

room is

115

Fig

Pressure-scanned The at 80 K. for the sample are indicated

11

Fig for

11

shows

5 dlfforenl

which

spectrum shown bwcond

lo

horo. by

the

Virtually are I

ono

ali

to

Rdmdn

dfld

Idttlce

two

hrgh

-

of

aro

variable

pressures

could

amblent

condltlon

spectra

qu110 expose

find

KBr/CaSOq

dre

The Iwo

rut-don

d

scanned

two

points

strong

Fermi-resonance

contain the

all

bands

redson

of

MI the

for

pressure

this

(II)

IS the

oxamplos

‘lattice

modes)

lniernal

mudu:. to

of

Fermt-resonance

assignments

contain

expected

side

which dre

band’

are

close

drdmdtlcaily

to

features

usually

too

weak

one-another

enhanvce

the

ln

to such

lntenslty

of

symmetry

general theso

many

of

19)

lhere

ds

exiernal

dpproprlate

tref

feature

speLtrd

sollds

be

tho

upsetting

dnd

can

to

band

Rdmdn

whurw

of

points

prossuros

slds

Internal

bdnds

dnd

spectrum

4bar

(1)

changes

thoreby

spectra of

rwondnce

side

Thbise of

dnd

Iiowover

Form1

soma

lnlenslty

the

7 3

dre

!b oxpociod

Ignored

of

1 and

study

Idtticw

Infrdred

confuslon

spectra

a

region

5

thl:.

reldtlve

comblnaitons

~dubt)

use

whore

usually

R

(brndry

dboul

IS due

wide

cm-l between

make

rdpld

bdnd

which

20

pressures

wish

I

a

Fermi resonance In the Infrared spectrum of KSr/CaSO4 narrow spectral range (1070 to 1090 cm-l) was recorded subjected to the five different pressures of hehum gas that

although elrects

roullne

lhey

dre

usually

IS the

basis

of

appllcahons

in

the

the

ignored

The

contentton

that

Inlerpretatlon

of

CONCWSIONS used

I high

much

pressure.

relatively

and

little

space

However characteristic lattice sufficient

side

of

the how for

I hope

reason

one

I

for

have

induced

features a

more

space

might

showing

that

pressure band

available

set

about

examples shown frequency

which

explaining

are

routine

of

use

doing what

enough

to

shifts.

relevant of

why

to

(ii)

so has

might

This already

support

the

left

wish

Idee

as

all an

to

me

been

work

at

with

done that

Fermi-resonance

virtually

pressure

one

spectra. experimental

(I)

and

(1111

constttute variable

a in

116

spectrnTcoplc Secondly research. pressure future

studies I hope that I have conveyed

where phase

the

Investigation

dlagrams

gsieratlons

must

some

of the ever

hold

many.

of the excrtement

expandlng

regfions

as yet unexpected.

of high

pressure

cf temperaturesurprises

In store

for

of scientists

ACKNOWLEDGEMENTS

1 gratefully acknowledge the flnanczal support gl\en by SERC, the Paul In;trumont facllnies

1. 2 3 4 5 H 7 8 Y 10

11

I.?

13 14 I’) lb 17 lb 19

W F

Fund at King’s

and

the

U S

Army

In setting

up the

high

pressure

spectrocoscoprc

College

Sherman and G R Wilkinson. Chapter 4 pp 158 to 336 vol 6. ‘Advances In Infrared and Raman Spectra’ CEds RJH Clark and RE Hester) Heyden. London C1980) _ W F Sherman. Bulletin de la Soclete Chlmique de France No 9-10. 1347 to 1369 C1982) W F Sherman and A A Stadtmuller. ‘Experimental Techntques in High Pressure Research’ to be publlshed by Wiley (1984) King’s College London (1982) A 4 Stadtmullar. PhD Thesis E Whalley. A Lavergne and P T T Wong. Rev Sci lnst . 47.845 (1976) Itav Scl lnst 52.962 C 19791 F Whalloy and A I avorgno. S lkawa and E Whatley. IX AIRAPT conference. Albany Cl9831 W F Sherman. J Scl lnst s-462. (1966) HA I--Ilch. r E Slykhouse and H G Dr1ckamer.J Opt See Am 47.1015 (1957). S Block and G Plermarml. Physics Today. 44 CSept 1976). R P Lowndes and A Aastogi. Phys Rev m-3598 (19781. M S Shdwyur dnd 31 F Shurmdn. Infrdrad Physics 18.909 C 1918) and 22. 23. C19821 King’s College London C1982) B Sukarova. PhD Thesis. B Sukarova. J Mel Srr 80.217 C 19821 W F Sherman and G R Wilklnson I> I) Kiu9 drld I Wtlcilluy IX AII(AI’I ~onluroncc. Albany C IYtlJl C_, J I’rorrndrrnr. It L Muriro dnd t Mock. IX AIItAI’T uunforoncc. Albany C lY83) P T T Wong and E Whalley J Chem Phys 64.2359 Cl9761 G I- Slark. A K Gdr9. W I- Strormdn and G ft Wilkinson. tUtihlOS XVI C 1983) S I CWIL dnd W I- Shormdn. Spoulrochlm Acta. 3a b fJ C 1979)