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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
THANK YOU
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