Studies of reversible and irreversible temperature effects in the infrared spectrum of matrix isolated ammonia and ammonia-d3

Chumicti

8 ( 1975) 185- 191

Physics

Q North-HaUand Publishing

STUDIES

Company

OF REVERSIBLE

IN THE INFRARED

AND IRREVERSIBLE

SPECTRUM OF MATRIX

I. Introduction Low

Icmprra[urc

I1 ) provides

malris

a powbility

nioleculcs

in Cir2umstxus

tronsl;ltion

and rotation

Recently, nique

a number

have dealt

ni3 molecules [Z-O].

isol2lion tti study

trapped

of single

whew irttluenccs xc prxfic311~*

of irwcs~i~crtions

with

sparroscop>

spcclra

riom

climina~d. usrng IIIIS wch-

~lte infrared

speilrum

m diffcrcnt

matrix

of ammorlllltCri3lS

Llos! of tlirsc 113w hwn concerned willi studsprctroscoplcal evidence for rotilImn

iss 01” possible

of rhc mppzd ammonia n~oleculds. Very r~ccnfly IWO invcst~galions IS.O]. using difkwnt techniques. lwe scf fled an old problcru 13.3 1 and proved

or invcrsian

~JKII rhe bands in 9 nitrogen

in the u2 region malris.

[ion of the isolstcd

molecules.

has been extended infrared

been studied

~sofutcd librs-

In this work zrrenrion

IO 311 w&ions of tire limdamcnkal of ummonia

transitions

Isted in a nitrogen Iwe

o( ammonia.

are not due lo roI3tionul

matris.

35 functions

K) and concentration.

and a~nn~onixI~

In addition

llwe

of tsmpcraturc

iso-

spectra (G-20

TEhiPERATURE

tSOLATED

AMMONIA

EFFECTS. AND AAfMONIAdI,

In order to increase Trans.%

polymer

smriionia

nealed (SC~ rd. b

[I

lo ;1 tempcr3tnre

the working

heIwWrl

TIte tzrrlpcr,+

temperature

I S-20

the spectrum

of a sample

several days [3,12]

of IOK

K for 3 Sllort iirnec,

min. The changes upon anncaliq

Z-5

20 K stem to be completed

J------

of dimer and lhe sample Iv35 an-

] under -‘diffusion”).

ture was raised iron, mostly

the arnounl

in tile matrix.

wirhin

up ro

3 few mlnut?S. and

kept I~I 20 I; is stable for

.

All infrared spectra were recorded on n Perkin Elmer /I3]. kp1

IS0 instrument The

3S COllSIilnl

perimcnr 40

3330

3320

3310

* 33OOcrri’

resolutions

calibrated

3s possible

regions were

from osperimsn~

to make comparisons

ful. The wavenumbers

with standard gss?j

used in difierenr

10 ~KL-

meanin! 1 and 2 xc bdieved~~

of interlsjll2s

in tables

be correct within

+O.S cm- 1, esccpt where orllerwiv

stated. Extcnckd

uncertainty

ed by difficulties

to find

intenals

are alWjC3~~

the exact position

ofbrojd

CT RibbGnlllR

spectra oJanrmoma

arrd at~~~~o~~~a.~:,

187

. 1625

rk. 3. (3) Tcmperaturc WR

= 100).

CITKIS in the UJ rqion

1610 cm"

of~mmoma

01/R

= 100).

(b) Tcmpcrawrc

cflcct\

rn 111c u3 rqion

of ammonra_d3

T;rble I Ammonia

in nitrogen

Wavcnumbcr km-’ I 3147.8 3440.9 3436.8 3431.6 3427.8

Absorbance M/R = 100 before and after anneal

?I I

I

3501.9 C3400 3330.6 3312.1 3308.1 3244.6 3235.2 32 16.5 : 1 3210.5 f I 1647.2 22 1637.9 1630.7 1623.1 1618.2 1609.0 1113.9

lO13.0 1003.2 9S5.7 969.2 965.1

:I

Tsblc 2 mdriv 3t 10 I<

0.06 0.37 KJ.09) 0.11

0.06 0.34 (0.07) 009

Kl.03) 0.04

KLcl3)

lO.O-1)

“3

01)

~3

(Mb

“3

flrl)

OB03 0.15 0.34 0.60 O.-l6

*1

131

I31 ID) 131 W 131 (;\I) 131 (D) 131

w) (D?) 131 3LLJ 01, (P) (P) UN’) [ 3 I “4 L’J

(11) II!) (31

“4

(hl) 131

hot bdnd q+vp i>l) 131

U? (0.05)

and

(cm

0.07

broad rugion 0.17 0.32 0.09 0.03 (0.07) IO) 0.08 0.03 0.09 0.08 (0.0-t) (0) (0.06) (01 (0.07) IO) 0.14 0.1-l 1.2 I .4 0.1-l 0.10 O.-t3 a.-12 0.03 0.18 0 0.32 (0.31) too liugc

Assignmrnls rcfcrcnccs

L.1

(P) (2.31 (0) 12.3.91 ID) 12.3.91 (51) [‘.3.5,91 (15Nli3)

In this region four bands were assigned 10 the drmer. bur some. ot’thcse assignments wre lenwivc. Probably more dirner and polymer bands are hidden under the v3 bands. For ammonin-t13 the ut absorption is very weak. The assignment of the band at 241 I .5 cm-’ 10 the dimer was made in analogy wl~h the results for nmmonla. Al 3235.2 cm-’ ;1wcJ and nxrow band NQS found. From US intensity behaviour it was assigned to the monomer. A comparison with the gas phase specIrum of ammonia suggests that the most likely assignment sl~ould be 7u4. In rhe gas phase this band was found 31 32 16.7 cm-1 (?~a) [ Id]. In ammonia-d3 ;1 corresponding absorption was detected at 1368.2 Cm-’

Ammonia,d3

in nitrogen rnatrL\ 3t IO 1;

!Vxcnumbcr km-’ )

Abtorbancc M/R = 100 before and LI~X anncal

3564.1 7559.5 2556.1 75s 1.6 3530.7 x233 X10.0 :I0 x15.9 XI 1.5 ‘-374.8 rl ‘368.2 1206.0 2 I 13OcJ.5 : I

0.13 0.46 0.40 m.08) 0.09 0 0 0.01 0 0.01 0.05 0 10.0-l) 0.12 0.65 lO.-‘3) (9.2R) 0.4 I

1195.3 1190.3 1188.9 rl 1185.9 1185.2 I 178.9 : I

0.1’ 0.41 0.31 (0.1

Assignmcnis reicrcnccs “3 “3 “3

I)

0.19 0.15 0.07 0.05 0.03

“I

0.42

Il.09

1’4

0.09

0.09

0.08

vz+up

0.33

CL-21

1’2

md

(Sl) (%I) W) (D) (DJ (P) W) (\I) (D) (D?) (Xl) (D.P)

(51) (DcrrP+

hot bsnd?)

891.5

:I

829.3 787.6 78 I .5 769.3 758.9 751.8

O.03 0.29 (0.39) 100 IXFc 0.03

(Xl) 15) (ND,Il.M)

(31 WG

W)

0.54 0.52

(D) (DI ‘?_‘I31 (“SD,)

0 OJ

tr._ “2

In this rqion 311 absorption bands seem IO be locat. cd wilhin 50 cm-’ bolh for ammonia and ammoniatl, (set figs. 4a and -Ib). Therefore no exhaustive assignment of dimcr and polymcrtc Howcvcr. irrevcrslblr changes

bands could be made. in the spectra could bc

dtscerned when wmling.

5. The reversihle temperature effects Revcrsiblc

IempCralure

the E-symmetrtcal

effects appcarcd only on

absorption bands (~3.

~4). Tltex

were split up in several sub-bands

We

was below 70 K. In

this

where the tcmpera-

work

bands in each

three

region for both xurncmta end amrnonizilj to derive from matrix isolated monomer. be more bands from the monomer here IL’SS intense extntple.

further

or [or

not

rcsohd

anintonia*lg

in

these

but

mio,ht

are

rksc

esperimonts.

For

::‘~\s3n &icatiorr

the

splittm_c 3t Ihc lowsl

were found ~bere

of (SW Q. qh).

temperaiuw

For both regions and both subsranccs the over& tern

~3s

the

sxne:

the

lnojt

dle, tile next intense band at 3 lower wve 3. markedly larger spht for rj4 snmP3red

number WltlI

Io 1’3 for IlIe

band at 3 hi&H

some subsIrrnce and the le.~st interw

VJW~ nu~~tbcr but willt ahout IIIC sme

split for v3 a)\1

p4 for Ihe ~3mc substance. The splittings amrlloni3

are Ixger

but 110 simple

than for ammonisi!;

Pat-

band in the mid-

mwnsc

for

isotopic

apply. At Ihe hi_clIer temperatures Illc bands merge IQ OIIC or Iwo bJ0dd $xorpIions. It relations

seem

should hc WI&

to

that 11~~total width of lhls 3bsorpciun

region is srnallcr tlian (lie ilisr3iW most low Iwipcr3turk?

ll?~NWfl

ltltt Ollll’r-

tion variation and annealing. The temperature reverS_ ible change also remains unexplained in terms of a~:,~. galion. An effwt from mult\ple trupping sites oud,I t0 &angc

on annaling

and slIould

nlso

of degensca r)’ done could account for only two bands per degcnp. rate vlbrarion.

bands. SplIItinR,

Tbercfore

tlIe explanation

that seenIs

most likely lrere is that the fine structure

is due 10 ,D. wit11 ~p\,~.

tational hbration, perhaps in conlbinution tine of’tl~e E-symmcIrical dcgencracy. As mentioned in tltc introduction no rotatioll,,l libation

rotarional

only couple with TlIe

fine

could be found in the “1 region. HoRw~J,~

structtrrt!

round tk

cumponents rotation.

symmetry

the E-symmetrical

frequency difiercnces

betwen

a~bsrricr

[

axis slIcJul~

wbrations

are 100 small to be compaible 3 lllree-fold

of tl~r COCWCL order oi ~~ouI

Iwighr

30 cm-

\vIIll jjrt

rotation

terms from

151 and Coriolis

FIVES splittines

[;I,

t1w tine sIrII;t~re

but some kind of restricted

be possible. A simple model wirl,

3 hurrier

~_~omponenls. It iS inrwstinf

irrcvrrsibly

split tile A-synIIIIetrlcal

Illl~_hr ro[;lIIon.

the ~3s pllaje

ol’ mapnitudc.

\yi~,

I flo\~~\yr. it waj

not pussibie to xcount

for 311 line structure

frared spcc[run\ hctwecn g.lj phxir: 31Id liquid solurioo.

nents using this model.

It seems likely tlIat ;I lIloJe e)2h,

A similar Icmper.IIure

0r3trd

to0 10 comp:Irz rllis bclwiaur

strucIur2

of an infrared

wrli

dependen

the hng5

m in-

effect on Ihe lint

band of matrix 13ola1cd CH3D

information

wx norized by Hopkins Ed al. [5

1. A small hot band was found at 1609.0 snl_I

uJ region ot’ammonia.

in IlIe

behavivur on annealing. A rouflI

mokcule

considering

* Signs oi 3 possible corre-

The ammonk

were

cm-l.

uudied

;ItOmS.

in t&k.

niaJ3 on infrared

bands of matrix

isolated

molecules IS u~uaIly csplsined with the followinp Possib(e effecI$

wIlI

one IIydrogen TllC

They

et al. [3].

;!I 110K ~2s

propog

bond linking

3 dlmer

1112I\~Onl.

rc5ulIs t’rom this inves\i-jgIiun are

consistent with their proposed diner structure ~UI~I: rise to anorll~Y possible assignment ior the dlmrr.X rencativc

dwr

Iwi\~cen [he

lattice could be sJin?d.

dimcr in solid nitrogen

by Pimentel

sIructure

Discussion

FAIR structure

the interactInns

its

trogen 6.

conwning

and the mutris

lil)ratioI\ nI~_e\~t

and in the process valujblc

estimate oi iIs XIIV~-

sponding overlapped hot band for amnronia/~ noriced at I179

of Ihe rolalional

It was Ioo small IO be safely 3s.

signed. but seemed tu be monomeric tion energy gave 9 cm-

description

csplain the l?nc structure

c”I,,po.

four

[I I. AggregarIon. 11nt is formation

anil paiymers; crystal effects

or

multiple

Pin? siIes; split of vibrational degeneraIi0n; IihratIon modes in tljc fwrr;,~.

of

trup.

mulecul3r

s4ynlanr

for

the ammonia dimer is_el\cn

3 and a corresponding

CM be r&e

assignmenr for ~INIIO.

using the data in table 7. Excep!

for minor differences in the frequzncres measured, which all could be esplained with ti smsll IC’III~LXIIU~~ shift from 7-0 to IO K and the uncerIainI?’ inIenr& proposed, the chief discrepancies

between IlIe ~SSI!~

ments in table

3 and ref. I31 are the foUowing. Fir@. in the complex the proton ncceptor sIllI ha lwX(C3~. symmetry

but the proton

try. Therefore

donor only local C,-sYmnl+

the E-degeneracy

for Ihe protondonfir

should be splir. This seems not IO IKW h+cn cdQp

Table 3 Tcntafiw -

as~?pmcnt

hlonomcr

(E):

3147.8

bands.This is, however, consistent with what should be expected using the dimcr structure proposed hcrc and lhe kind of force liclds rnentloncd above.

ri,r Lhc ammoma dimer -__ Dimcr

(A”):

3440.9 3-13t .6

(Ix):

0,).

3330.6

(A, I.

E):

1637.9

_ 3350

33LL.l

(A’):

3301.9

(A’):

3145.6

(A”): 02):

1630.7 1618.2

Acknowledgement

-3110

This work MS supported by the Swedish Natural Science Research Council and the HoyA Phys~ographic SotMy in Lund.

- 1630

- 16311 (A’):

References

In

rsbfe

3

lllc

beled 3s one with

IWO

mokcuks,

C 3y-s~mme10.

in

111s

dimcr,

lhe proton

(1rz [a-

acceplor,

aud QRL with C,-symmetry. the proton donor. Thosr: dimer bands which are believed to be hidden in the Esymnctrica~ Egiuns of the monomer hands. are on)) indicated in tlie tables. The assienmcnt that is proposed here is consistent with \vhaI could be espccted from two separate ammonln molcculcs linked together with a I>ydrogen bond and with their internal rorcc &Ids only sligh0y pcriurlatcd. Tursi and N&on. in their mvcstigation of the ~v;lter dimer in ;1 nitqen matrix [ 16j. proposc a dimcr s\ruc. turc! with orw hydrogen bond linking the two oxygen atoms, analogous to the dimcr struaure proposed for ammonia, For thz two dimcr cases. water and ammo. rria, rile frequency shifts, monomer IO dimer. stem to agree both in dlrcction and or&r of magnitude vkrever comparisons could be made. III tlrc E-spwztrial bend region (v,) oi smmania and ~mmoni~-d3 311dimer bands seem to be overlapped with the monomeric

151 tt f fiopkins, RI. Curl and KS. Pltzer. I. Chcm. P\I~s 48 (1968) 2959. 161 L. At~ou~f%rguin. It. Duboar snd F. Lcgay.Chem. phy~. Lcfws 7 (1970) 61. 171 L. r\bou.&Marguin end If. I)uborr,Chcm. Phyc. Lcrrcrs 15 (1971) 445. 181 L. Aboual-Uargum. II. Uubort and I Lcgay, (‘hem. Phys. Lclrrrc 23 (1973) 603. 191 IA. Cuglcy and A.D.F. PuUm, Spccrrochim. ACID 29~ (1973) 1665. I tOj L. Trcdin, Sj. Roscngrcn and S. Sunncr, Chcmrc;l ScrIPta 4 11973) 93. (I iI 1..TreJm, Chemic2 Swprs 5 I197.f) 193. 1121G. Ribbe$rd, Chew. Phys. Lrrtcrs 25 0971) 333. 1131 IX. Plylcr, A. Dante. L.R. Bl~inc and E.D. T~d~ell. J. Rescxch NBS 64 (1960) 29. 1141 \t’.S. Bcncd~. E.E. Plpkr Jnd IX. Pltys. 32. (1960) 33.

Tidacll.

J. Chom.