THE ELECTRONIC SPECTRUM OF JET-COOLED H2PO, THE PROTOTYPICAL PHOSPHORYL FREE RADICAL

Mohammed A. Gharaibeh and Dennis J. Clouthier

Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055

Ricardo Tarroni

Dipartimento di Chimica Fisica ed Inorganica, Università di Bologna, Viale Risorgimento 4, 40136

Bologna, Italy

Background

Phosphoryl radicals are important intermediates in organic synthesis and polymerization processes. H2PO is one of the many products of the oxidation of phosphine

No previous studies of the electronic spectrum of the H2PO free radical

Microwave spectrum of this molecule was reported in 1996 [T. Hirao, S. Saito, and H. Ozeki, J Chem Phys 105 (1996)]

Studying the periodic trends in the heavy atom nitroxyl radicals which have the general formula H2XO where X is phosphorus or arsenic atom

The dihydrophosphoryl radical (H2PO)

H2XO ground state structure (X=N,P and As)

15A

Cs

Cs

C2v

Dihydronitroxyl radical

Dihydroarsenyl radical

Dihydrophosphoryl radical

π*

π

n

a'

a''

a'

a'

π*

π

n

a'

a''

a'

a'

π*

π

n

a'

a''

a'

a'

Ground State

1st Excited State

2nd Excited State

T0 = 11200 cm-1 T0 = 26700 cm-1

Theoretical calculations / MO diagram

CCSD-EOM / aug-cc-pV(T+d)Z

X 2A~ A 2A~ B 2A~׳ ׳׳ ׳

Theoretical calculations / geometry

Calculated molecular geometries

π*

π

oop:

Oθ

P

HH

X 2A′ B 2A′

CCSD/ EOM-CCSD/

aug-cc-pV(T+d)Z aug-cc-pV(T+d)Z

r (P-O) Å 1.487 1.654

r (P-H) Å 1.407 1.417

q (HPO) o 114.6 105.8

q (HPH) o 102.4 92.4

q (oop) o 48.3 66.9

~ ~

Production of jet-cooled H2PO radical

Pulsed valve Ring electrodes Reheat tube

Vacuum (~10-6 torr)

40-100 psi of5% PH3 + 4%

CO2 in Ar

HV

40-100 psi of5% PD3 + 4%

CO2 in ArH2PO D2PO

Low resolution LIF spectra

ν2: PO stretch

ν3: HPH sym bend

ν4: HPH wag

Observed isotope shift = 11.4 cm-1 Calculated Isotope shift = 17 cm-1

Emission spectra

H2PO

D2PO

ν2: PO stretch

ν3: HPH sym bend

ν4: HPH wag

Vibrational constants

H2PO

D2PO

ν2: PO stretch

ν3: HPH sym bend

ν4: HPH wag

Calc = CCSD/aug-cc-pV(T+d)Z

State Parameter (cm-1)H2PO D2PO

Obs. Calc. Obs. Calc.

X2A′

ω1 (PH stretch) 2221.4(9) 2403 1576.5(7) 1719

ω2 (PO stretch) 1163.4(5) 1190 1141.2(2) 1173

ω3 (HPH bend) 1085.9(5) 1135 795.7(6) 821

ω4 (HPH wag) 783.6(3) 788 595.5(5) 600

B2A′

ω1 2321.9(4) 2361 1601.5(1) 1693

ω2 790.7(3) 843 904.3(1) 983

ω3 1073.7(3) 1132 781.0(2) 825

ω4 1027.0(4) 1076 672.47(5) 692

~

~

32

4321

4321

D

HH

D

D

H

H

D

m

m

M

M

B

B

Ground state 0.388 : 0.388 error = 0.0%

Excited state 0.376 : 0.385 error = 2.3%

Teller-Redlich product rule

w: fundamental frequencyB: B rotational constantM: total mass of the isotopologuem: atomic mass of H or D

Frequency ratio Mass ratio

Strong a-type transitions

Weak c-type transitions

A′ A′ = A′

Cs E h linear functions, rotations

A' +1 +1 x, y, Rz

A'' +1 -1 z, Rx, Ry

Rotational band types

Transition moment vector

c=x

a=y

H

P O

High resolution LIF spectrum of the 00 band 0

High resolution spectrum of H2PO

Rotational constants

State Constant (cm-1) H2PO D2PO

X 2A¢

A 5.2077(1)* 2.6862(28)

B 0.6341107(3)* 0.5721(11)

C 0.5944851(3)* 0.5087(9)

B 2A¢

A 4.6186(13) 2.4115(21)

B 0.5142(5) 0.4705(12)

C 0.5036(5) 0.4495(12)

T0 26583.862(5) 26572.154(5)

* Microwave spectrum (T. Hirao, S. Saito and H. Ozeki, J. Chem. Phys. 105, 3450 (1996))

εaa = -0.044 cm-1″

HH

OP

HH

OP

=102.6 ˚

=115.5 ˚

r =1.488Å

r =1.429Å

=93.3˚

=105.68 ˚

r =1.671Å

r =1.4

28Å

Ground state Excited state

oop=46.5o

oop=70.7o

Molecular geometry

[1.407]

[1.487]

[114.6]

[102.4]

[1.41

7]

[1.654]

[105.8]

[92.4]

[66.9][48.3]

Oθ

P

HH

Oθ

P

HH

CCSD-EOM / aug-cc-pV(T+d)Z

Geometry: H2PO vs H2AsO

State r (X-O) r (X-H) q (HXO) q (HXH) q (oop) T0

H2PO

X 2A¢ 1.488 1.429 115.5 102.6 46.5 0

B 2A¢ 1.671 1.428 105.68 93.3 66.8 26583.86

 Change 0.183 -0.001 -9.82 -9.3 20.3  

H2AsO

X 2A¢ 1.672 1.513 106.6 101.8 63.1 0

B 2A¢ 1.806 1.525 103.1 93.4 70.7 19613.54

 Change 0.134 0.012 -3.5 -8.4 7.6  

Summary

• The previously unknown electronic spectrum of the H2PO free radical has been identified in the 407 - 337 nm region.

• The ground and the excited state a′ vibrational frequencies have been determined for H2PO and D2PO.

• The molecular structure of H2PO in the second excited state has been determined by rotational analysis of the 00 band.

0

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