INFRARED SPECTROSCOPY OF H3O+(N2)n (n=1,2,3) COMPLEXES.

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Infrared Spectroscopy of
H3O+(N2)n (n=1,2,3) Complexes
Tim Cheng
Biswajit Bandyopadhyay
Michael A. Duncan
Department of Chemistry, University of Georgia, Athens, GA 30602
NSF
Proton affinity of water: 165.2 kcal/mol
Proton affinity of Nitrogen: 118.0 kcal/mol
Experimental binding energies for H3O+(N2)n
by El-Shall and coworkers1
n=1: 7.8 kcal/mol (2730 cm-1)
n=2: 7.3 kcal/mol (2553 cm-1)
n=3: 6.3 kcal/mol (2203 cm-1)
J. R. Roscioli, L. R. McCunn, M. A.
Johnson, Science, 2007, 316, 249
1
R. Mabourki, Y. Ibrahim, E. Xie, M. Meot-Ner, and M. Samy El-Shall, Chem. Phys. Lett. 424, 257 (2006).
Experimental Setup
LaserVision OPO/OPA with AgGaSe2 crystal.
Continuous coverage throughout the midinfrared (4500-800 cm-1).
Linewidth ~2 cm-1
Mass Spectrum
+
1
H (H2O)n
4
+
H (H2O)(N2)n
4
Relative Intensity
1
0
20
40
60
80
m/z
100
120
140
160
DE
3
3519
3602
+
H O -N2
Experimental- Loss of N2
2787
3031
Theoretical
1000
1500
2000
2500
cm
-1
3000
3500
4000
+
H3O (N2)n
3110
n=3
3347
2600
2800
3000
2957
3200
3400
3600
3800
n=2
3585
3208
2600
2800
3000
3200
3400
3600
3519
3800
3620
n=1
2787
3031
2600
2800
3000
3200
cm
-1
3400
3600
3800
Shared proton potential
rp
H2O.......H+.....N2 shared proton potential
calculated in MP2/aug-cc-pVDZ level of theory
Energy(Kcal/mol)
30
20
-1
E0 (cm )
E1
E2
E1-E0
1389
3879
5873
2490
10
0
-0.5
0.0
0.5
rp-r0(Å)
Expanded View of n=1 with rotational
simulation
3591
+
3519
3579
(0,1)
H3O -N2
3620
(1,2)
Experiment
3600
(1,0)
A'' = 9.45 cm
3566
(2,1)
3661
(2,3)
3510
3600
B'',C'' = 0.13, 0.13 cm
3690
Simulation
A' = 9.75 cm
B.O.
3600
-1
cm
3690
-1
-1
Tj,k = 20, 40 K
B.O.
3510
-1
asym
sym
= 3591 cm
= 3518 cm
-1
-1
H3O+N2
3591
3629
(0,1)
3691
3629
Li+(H2O)Ar
(2,1)
(2,1)
(0,1)
experiment
experiment
(1,0)
(1,0)
(1,2)
(3,2)
(0,1)
(3,2)
(4,3)
(2,1)
(0,1)
(2,1)
simulation
(1,0)
simulation
(1,0)
(3,2)
(4,3)
(1,2)
3500
3600
3700
3800
cm
A'' = 13.4 cm-1
B'',C'' = 0.07, 0.07 cm-1
A' = 14.3 cm-1
Tj,k = 15, 40 K
B.O.asym = 3692 cm-1
B.O.sym = 3629 cm-1
-1
(1,2)
3900
4000
(3,2)
(4,3)
3500
3600
cm
3700
-1
A'' = 9.45 cm-1
B'',C'' = 0.13, 0.13 cm-1
A' = 9.75 cm-1
Tj,k = 20, 40 K
B.O.asym = 3591 cm-1
B.O.sym = 3518 cm-1
Bending potential
Bending potential of the n=1 complex calculated
in MP2/aug-cc-pVDZ level of theory.
-1
Barrier Height (cm ) 757
Energy(Kcal/mol)
8
E0
438
E1
508
E2
1078
E3
1565
4
0
80
160
Inversion angle
240
Conclusion
• The shared proton stretch on hydronium shifts blue
from the n=1 to the n=3 complexes
• For the n=1 complex, partially resolved rotational
band is observed which gives structural information
• Combination bands were observed for all infrared
spectra with the shared proton coupling with the NN translation motion

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