Detection and Structural Characterization
of Nitrosamide H2NNO: A Central
Intermediate in de-NOx Processes
Michael C. McCarthy
Harvard-Smithsonian Center for Astrophysics
Kelvin Lee
School of Chemistry, UNSW
John F. Stanton
Institute for Theoretical Chemistry, Department of
Chemistry, The University of Texas
Talk MG02
ISMS, 70th Meeting, June 2015
Champaign-Urbana, Illinois
Motivation (post-facto)

First intermediate formed in the NH2 + NO reaction, which
ultimately produces one of three product pairs:
N2H + OH, N2 + H2O, or N2O + H2;
of key important in thermal de-NOx processes

Is the simplest N-nitrosamine; basis for understanding
how specific substituents subtly change the structure of
the NNO unit in larger compounds, 90% of which are
carcinogenic. Molecular structure is thought to affect
biological activity
Previous theoretical & experimental work
The NH2 + NO reaction has been the subject of extensive theoretical
studies and direct kinetic measurements; much effort focused on PES,
T dependence, and product branching ratios
Diau & Smith JCP (1997); Fang et al. Fara. Disc. (2001); Sun et al. JPC A (2005)
Initial step is exothermic, barrierless association to form H2NNO;
subsequent re-arrangement of this energetic intermediate ultimately
leads to products
Planarity of H2NNO remains open question; sensitive to level of theory
R
R
N—N
R
O
biradical
R
+
—
N—N
Ozwitterion
Lifetime in gas-phase estimated to range from >10-4 s to as short as 10-11 s;
only its infrared spectrum in low T matrices and mass spectrum reported
to date
Crowley & Sodeau JPC A (1990); Jacox & Thompson JCP (2005)
Potential energy surface
Fang et al. Faraday Disc., 119, 207 (2002)
Key findings
• Detect intense low-J, a- and b-type rotational lines; the full
gamut of spectroscopic constants derived to high precision
• All 6 singly-substituted species and D2NNO detected as well
• Experimental molecular structure (r0) derived; N—N bond
length roughly midway between two limits
• New CCSD(T) calculations predict planar and non-planar
geometries isoenergetic, a clear indication that the
torsional potential is extremely flat
Experimental approach
Cavity FTWM (5-43 GHz) + pin-hole nozzle +
electrical discharge
Q ~ 40,000
movable
mirror
1 msec
FID ~100 msec
cooled to 77 K
FFT
Use double resonance to
extend frequency range (5200 GHz+)
Combination: rapid formation and
stabilization of rotationally cold molecules
in multiple minima on PES; Tvib may be
much higher
An unsuccessful search for HNOO, but…
cluster of unidentified lines;
structure suggestive of carrier with
2 N atoms
23980
23984
23988
Relative Intensity
Frequency (MHz)
H2NNO or H2NON ?
NH3 + O2
NNO + H2
NH3 + NO
~48% H2NNO
~48% D2NNO
~1% HDNNO
~1% DHNNO
Intensity of 23069.6 MHz line
NH3/ND3 + NO 
D
77132
77135
77138
Frequency (MHz)
*
2
FT
50
-100
0
100
Offset (kHz)
DR
2
2
Doppler
1
25
E/h
(GHz)
0
1
E/k
(K)
1
J=0
0
Ka=0
Ka=1
23068
23069
23070
Frequency (MHz)
23071
Obligatory Table of Constants
Ht atom located furthest
from plane in nonplanar geometry
Constant
(MHz)
H2NNO
H215NNO
H2N15NO
H2NN18O
A0
80993
80603
78044
79842
79336
66591
64889
B0
12876
12513
12874
12201
11795
12525
11532
C0
11108
10831
11051
10583
10273
10544
9799
D0a
0.0075
-0.0000
0.0017
0.0012
-0.0256
-0.0084
-0.0378
Dea,b
-0.0458
-0.0464
-0.0458
-0.0458
-0.0661
-0.0563
-0.0766
D0-D0,na,c
…
-0.0075
-0.0058
-0.0063
-0.0331
-0.0159
-0.0453
De-De,na,c
…
-0.0060
0.0000
0.0000
-0.0203
-0.0105
-0.0308
HcDtNNO DcHtNNO
D2NNO
a Units:
b Non-planar structure calculated at CCSD(T)/CBS limit
amu Å2
cD
0,n and De,n refer to normal isotopic species
De only reflects deviations from planarity; D0 includes these, as well as zero-point vibration
Structural Determination (r0)
Hc
assuming planarity
117.5(3)°
113.67(3)°
116.3(5)°
Ht
Molecule
N—N (/Å)
N—O (/Å)
Comment
N2
1.098
----
triple bond
NO
1.15
NNO
1.127
1.185
HNNH
1.21
----
H2NNO
1.340(3)
1.219(2)
H2NNO2
1.381
1.231
H2NNH2
1.449
----
double bond
single bond
Structural Comparison
Parameter
Experiment (r0)
Theory
Planar
Non-planar
Non-planar
CCSD(T)/CBS
rN-O
rN-N
ONN
rN-H(cis)
NNH(cis)
rN-H(trans)
NNH(trans)
qONNH(cis)
qNNH(cis)H(trans)
1.217(3)
1.342(3)
113.67(5)
1.010(3)
117.5(3)
0.991(4)
116.3(4)
0
180
1.217(2)
1.342(2)
113.67(4)
1.010(2)
117.5(4)
0.992(3)
116.3(3)
0
175.2(8)
1.217(2)
1.342(2)
113.66(4)
1.010(2)
117.5(2)
0.991(4)
116.3(4)
3.5(6)
180
1.215
1.328
113.74
1.012
118.63
1.003
116.43
7.40
164.62
rms deviation
0.0076
0.0060
0.0062
…
Indication of
non-planarity?
Planar vs. non-planar
Non-planar:
Basis set
CCSD[T]
HF
Corr. Contr.
cc-pVTZ
0.03703703704
-185.5860334
-184.9055077
-0.6805257271
cc-pVQZ
0.015625
-185.6444701
-184.9202779
-0.7241922018
cc-pV5Z
0.008
-185.6637158
-184.9240233
-0.7396925064
-184.9245388
cc-pV6Z
Extrapolated Contribution
Extrapolated CBS Energy
-0.7560132806
-185.6805521
Planar:
Basis set
CCSD[T]
HF
Corr. Contr.
cc-pVTZ
0.03703703704
-185.585851
-184.9054551
-0.680395892
cc-pVQZ
0.015625
-185.6444215
-184.9202554
-0.7241661437
cc-pV5Z
0.008
-185.6636952
-184.9240107
-0.7396844944
cc-pV6Z
Units: Hartrees
-184.924527
Extrapolated Contribution
-0.756046339
Extrapolated CBS Energy
-185.6805733
4.6 cm-1
Vibrational Frequencies
Mode
1
2
3
4
5
6
7
8
9
Non-planar
pVTZ
338.2098
615.4078
685.1431
1077.941
1238.684
1570.696
1594.045
3503.963
3715.698
Planar
pV5Z
pVTZ
pV5Z
200.8726 235.2452i 147.2882i
630.5532 624.1773 633.2187
697.4076 628.4838 703.7744
1103.419 1115.358 1108.038
1238.201 1233.325 1233.349
1562.981 1572.176 1558.693
1597.485 1595.457 1595.847
3508.282 3522.088 3513.032
3729.266
3751.06 3739.506
Calculated at CCSD(T); harmonic approximation
Final Thoughts
• Yet another example where the initial intermediate
in a bi-molecular (radical-radical) reaction has been
“trapped” (in high abundance) and structurally
characterized
• Searches for remaining isomers now underway; four
possible cis, trans-HNNOH conformers
• Studies of R1R2NNO may be worth pursuing to
determine change in N-N bond length
Acknowledgments
Marie-Aline Martin-Drumel
Kyle Crabtree
Oscar Martinez, Jr.
Carl Gottlieb
Sam Palmer
Paul Antonucci
NASA/ARC
Australian-Harvard Club
Previous experimental work