1. The rotational spectrum of the urea isocyanic acid complex
John Mullaney Newcastle University

2. Urea Important uses in a wide range of industries
Biologically important
Potential candidate for intermolecular bifurcated hydrogen bond

3. Experimental
- Laser ablation with Nd:YAG, 532 nm, ~20 mJ per pulse to generate urea in gas phase - 1:1 copper to urea rods - Urea monomer signal significantly weaker using pure urea rods
- Rod is constantly rotated and translated
~18 h
~36 h

4. Chirped-pulse Fourier transform microwave spectrometer (CP-FTMW)
- Nd:YAG laser ablates composite rod (copper and urea) - Argon carrier gas, 6 bar - Expansion in supersonic jet, gas sample passes over rod
Vacuum chamber
N. R. Walker et al., Phys. Chem. Chem. Phys., 16, 2014, 25221

5. 60 50 40 30 20 10
424k averages, ablation of a 1:1 copper to urea rod with backing gas of Ar at 6 bar

6. J=11-10 urea-isocyanic acid60
J=11-10 urea-isocyanic acid 50 40 30 20 10
424k averages, ablation of a 1:1 copper to urea rod with backing gas of Ar at 6 bar

7. Exp.
ab initio [CO(NH2)2]2
planar
A0 / MHz
(11)
4615
5229
B0 / MHz
(14)
C0 / MHz
(16)
Δo / u Å2
-1.472
Pa / u Å2
Pb / u Å2
Pc / u Å2
0.7364
Initial search for urea dimer
Inertia defect suggests planar structure
Large disagreement with calculations

8. - Urea known to thermally decompose to form isocyanic acid and ammonia
- Similar experiments with imidazole (WC08) showed that fragments are formed - Fragments detected in previous experiments are usually CN containing, e.g. CH3CN
- Urea known to thermally decompose to form isocyanic acid and ammonia
532 nm, Nd:YAG ~ 20 mJ/pulse

9. (H2N)2CO - HNCO
Exp.
B3LYP-D3/aug-cc-pVTZ
A0 / MHz
(11)
B0 / MHz
(14)
C0 / MHz
(16)
Pa / u Å2
Pb / u Å2
Pc / u Å2
0.7364
0.6334
Good agreement with calculation
Measurements of isotopologues necessary

10. (H2N)2CO - HNCO
(H2N)213CO – HN13CO
(D2N)2CO - DNCO
(H2N)2C18O – HNC18O
A0 / MHz
(11)
(17)
(97)
9999.3(16)
B0 / MHz
(14)
(12)
(15)
(20)
C0 / MHz
(16)
(13)
(16)
(16)
DJK / kHz
2.70(60)
2.27(15)
2.63(15)
2.36(17)
DJ / Hz
177.2(24)
182.2(23)
154.7(25)
162.8(32)
d1 / Hz
-14.7(37)
-15.1(28)
-14.2(36)
-15.7(42) N 24 20 27 21
σ / kHz
10.3
8.7
13.6
13.3
- 12 isotopologues of urea isocyanic acid, (H2N)2CO – HNCO, were measured

11. rs - isocyanic acid monomer*
B3LYP-D3/aug-cc-pVTZ
MP2/aug-cc-pVTZ
rs - isocyanic acid monomer*
r(O---H) / Å
1.8196(66)
1.7531
1.7320 -
r(CO) / Å
1.1657(32)
1.1696
1.1774
1.1664(8)
r(NC) / Å
1.215(14)
1.2045
1.2152
1.2140(24)
r(NH) / Å
1.024(17)
1.0336
1.0343
0.9946(64)
1.277(33)
1.2303
1.2325
NCO / o
166.8(22)
174.0
173.2
172.6(27)
CNH / o
119.7(24)
129.2
128.2
123.9(17)
* - K. Yamada, J. Mol. Spec., 79, 1980, 323.

12. Conclusions
- Measured the rotational spectrum of urea – isocyanic acid Hydrogen bonding interaction present Future work investigating other organic dimers/metal containing complexes/heavier complexes

13. Acknowledgements
Newcastle University Nick Walker Chris Medcraft Dror Bittner Luke Lewis-Borrell Bernard Golding University of Bristol Tony Legon