The Rotational Spectrum and Hyperfine Constants of Arsenic Monophosphide, AsP

Flora Leung, Stephen A. Cooke and Michael C. L. Gerry

Department of Chemistry, The University of British Columbia,

2036 Main Mall, Vancouver, B. C. Canada, V6T 1Z1

Introduction• All intergroup 15 diatomics have been

spectroscopically studied. Hyperfine structure for PN(a), SbN, SbP(b), BiN, BiP(c) has been observed.

AsP• 1969: 12 red-degraded bands were

observed. Suggested to be the 1 - X1 system.(d)

• 1970: Rotational analysis of the observed bands.(e)

a Raymonda & Klemperer, J. Chem. Phys. 1971, 55, 232b Cooke & Gerry, PCCP, 2004, 6, 4579c Cooke, Michaud & Gerry, J. Mol. Struct. 2004, 695, 13

d Yee & Jones, Chem. Comm. 1969, 586e Harding, Jones & Yee, Can. J. Phys. 1970, 48, 2842

Prediction of AsP Transition Frequencies.

• Based on rotational constant of Harding, Yee and Jones, Be = 5771 MHz.

• DFT QZ4P/SAOP calculations provided an estimate for eQq(75As) = -247.7 MHz

AsP

Portion of spectrashown required 1000 avg. cyclesand is displayed asa 4k transformation.

Transitions shown are from J = 1 - 0 rotationaltransition. The groupon the left is from withinthe v = 0 state, that on the right from within the v = 1 state.

Data Set• AsP has only one isotopomer.

• Hyperfine structure from As (nuclear spin, I = 3/2).

• Magnetic hyperfine structure from P (nuclear spin, I = 1/2).

• J = 1 - 0 and 2 - 1 transitions were observed in the vibrational ground state and first excited vibrational state.

Equilibrium Spectroscopic Parameters for AsP

Parameter AsP

Be / MHz 5768.07932(92)

e / MHz 23.96044(90)De / kHz 2.17(13)

eQq(75As) / MHz -249.0963(75)CI(75As) / kHz 25.6(7)CI(31P) / kHz 23.6(2)

Equilibrium Bond Lengths of Group V Phosphides

Molecule Bond Length / Å

PN 1.4909a

P2 1.8934b

AsP 1.9995SbP 2.2054c

BiP 2.2962d

AsP equilibrium bond length:e

e BCr 2

2

17

2 810

AhNC

re(AsP) = 1.99954398(16) Å

a Ahmed & Hamilton, JMS, 1995, 169, p.286b Rao & Laksham, IJPAP, 1970, 8, p.617

C Cooke & Gerry, PCCP, 2004, 6, p.4579d Cooke, Michaud & Gerry, J. Mol. Struct, 2004, 695-696, p.13

r(P-H) in PH3 = 1.42Å

“Triple-bond covalent radii”

0.54 Å

0.94 Å

1.06 Å

1.27 Å

1.35 Å

Pekka Pyykkö, Sebastian Riedel and Michael Patzschke

Chemistry: A European Journal, 2005, 11, p.3511

“A coherent bond length amplified by some 24 character in the wave function will form an entrance ticket to the data set”

Empirical Relationships for AsP:2

2 16

e

eeeee B

Bx

Parameter This Work Previous Expt’sa

e / cm-1 627(18) 604.02

exe / cm-1 2.04(8) 1.98

a Harding, Jones & Yee, Can. J. Phys. 1970, 48, 2842

e

ee D

B34

Force Constants and Dissociation Energies for the Group 15 Phosphides

2)2( ek ee

ediss x

E

4

2

.

For AsP:

k = 507 Nm-1 and Ediss. = 576(40) kJ mol-1

lit. val. D00 = 430 kJ mol-1 (a)

a Gingerich, Cocke & Kordis, J. Phys. Chem. 1974, 78, 603

Force Constants and Dissociation Energies for the Group 15 Phosphides

200300400500600700

200 400 600 800

Diss. Energy (kJ/Mol)

Forc

e. C

onst

. (N

/m)

HRMS

Mass Spec.(a)

BiP

SbP

AsP

P2

PNPN

P2

AsP

SbP

BiP

For the Morse potential k = 22Ediss.

a Gingerich, Cocke & Kordis, J. Phys. Chem. 1974, 78, 603

Hyperfine Constants

eQqe(75As) value in AsP = -249.0963(75) MHz(DFT value = -247.7 MHz)

eQq(X) / MHz q(X) / 1022 V m-2

PN (X=N) -5.1416(5) -1.040(2)

AsP (X=As) -249.0963(75) -3.28(6)121SbP (X=Sb) 617.4417(41) -3.82(9)a to -7.1(9)b

BiP (X=Bi) 898.2172(46) -7.20(22)

a Using most recent literature value for Q, (= -66.9(15) fm2): Svane, Phys. Rev. B, 2003, 68, 64422.b Using Q (= -36(4) fm2) value tabulated by Pyykko, Mol. Phys. 2001, 99, 1617.

-8

-6

-4

-2

0

Fiel

d G

radi

ent (

10^2

2 V

/ m)

PN AsP SbP BiP

Field Gradients at the non-phosphorus nucleus in thegroup V phosphides.

(PP)

Using DFT we calculated q at Sb in SbP to be - 4.7 1022 V m-1.

Our results suggests a better value for Q(121Sb) of ~ 50 fm2.

Using Q(121Sb) = -66 fm2

Using Q(121Sb) = -36 fm2

Vibrational Dependence of eQq

• For all of the group V phosphides for which appropriate data is available:

• Electronic ground states have asymptotes corresponding to atomic ground states of 4S3/2 for both atoms (i.e. an s2 p3 configuration)a.

• Increase in v → step toward this asymptote, at which point q at each atom is zero.

|eQq| ↓ as v ↑

a Alekseyev, Liebermann, Hirsch & Buenker, Chem. Phys. 1997, 225, p247

eQqv=0(75As) = -247.9495(46) eQqv=1(75As) = -245.6560(61)

31P Nuclear Spin-Rotation Constants

Molecule CI (P) / kHz 106 CI (P)/ Be

PNa,b 78.2(5) 3.31AsP 23.6(2) 4.09SbPc 21(3) 4.98BiPd 23.7(6) 6.67

a Ahmed & Hamilton, JMS, 1995, 169, p.286b Raymonda & Klemperer, JCP, 1971,55, p.232

C Cooke & Gerry, PCCP, 2004, 6, p.4579d Cooke, Michaud & Gerry, J. Mol. Struct, 2004, 695-696, p.13

05000

100001500020000250003000035000

3 4 5 6 7

Ab initio ValueToscano et al. ZPD, 1992, 22, p683

31P Nuclear Spin-Rotation Constants

106 CI (P) / Be

3 + -

1 + E

nerg

y Se

para

tion

/ cm

-1

PN

AsPSbP

BiP

01

1WWB

C

e

I

Where W1 - W0 is the energy gap between the ground

and first excited electronic states, a3+ - X1+.

Expt’l values: Rasanen et al. JCP, 1986, 85, p86Briedohr et al. JMS, 1995, 172, p369

CInuc depends only on the nuclear positions.

CIelec depends on the ground and excited state wave functions.

Similarly: av = p + d

d depends on the ground state wave function.p is directly proportional to CI

el.

The relationship between CI and shielding constants

Flygare & Goodison:

elecI

nucII CCC

As and P Nuclear Spin-Rotation Coupling Constants

More directly CI may be related to the span of the shielding tensor:

IeNe

p CBgm

m

2

75As 31P

CI / kHz 25.6(7) 23.6(2)p / ppm -2895(74) -1262(8)d / ppm 2920 1112av / ppm 25 -150 / ppm 4070(110) 3756(29)

calc. / ppm 5061 2391CI calc. / kHz 30.4 33.9

||

DFT calc.

Conclusions• The pure rotational spectrum of AsP has been recorded for

the first time.

• eQq(75As) has been determined in AsP and compared with other known eQq values in related molecules. The comparison suggests an anomaly in Q(Sb).

• Nuclear spin-rotation coupling constants have provided useful electronic structure information for the series of Group 15 phosphides.

Acknowledgements

UBC Mech. And Elec. WorkshopsThe Natural Sciences and Engineering Research Council of Canada (NSERC)