American Geophysical Union, General Assembly. 10-20 December 2012, San Francisco (USA)
Adsorption of glyoxal molecules
on atmospheric water ice nanoparticles
O. Schrems , S. K. Ignatov1,2, and O. B. Gadzhiev1,2
1
(1)Alfred Wegener Institute for Polar and Marine Research in der Helmholtz-Gemeinschaft, Bremerhaven (Germany)
(2)Department of Chemistry, N.I. Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod (Russia)
Introduction
Experimental
The understanding of the uptake and incorporation of atmospheric trace gases in
water ice as well as their interactions with water molecules is very important for the
understanding of processes at the air/ice interface. Trace gases trapped in snow, in
ice particles or at ice surfaces may be subject of photochemical reactions when
irradiated with solar UV radiation. In the study reported here, we focused on glyoxal
(HCOCHO), its interaction with H2O molecules and ice, and its photochemistry when
trapped in an ice or argon matrix. Glyoxal, an atmospheric relevant carbonyl
compound is the simplest a-dicarbonyl and is formed as product in the
photooxidation of simple volatile organic compounds in air in the presence of NOx.
Few measurements of glyoxal have been reported with mixing ratios ranging from
100 ppt to a few ppb. Glyoxal exhibits an absorption spectrum consisting of two
main absorption bands: a broad UV band between 220 and 350 nm and a stronger
structured band in the range 350-480 nm.Theoretically, the photolysis of glyoxal can
occur through the following channels:
Glyoxal was prepared by decomposing its trimer hydrate at 150-160^C in the presence of
P2O5 and under a N2 flow. It was collected as yellow crystals at -20°C. and stored at -20°C.
In laboratory experiments we have simulated the UV photochemistry of glyoxal (HCOCHO)
trapped in ice (at 14 K) and for comparison in the gas phase and in solid argon matrices.
The low temperatures have been obtained by means of a closed-cycle helium refrigerator.
The photoproducts formed in the ice have been identified by means of FTIR spectroscopy.
The photolysis experiments were carried out with a Xe/Hg deep UV lamp (Ushio UXM -502
MD) which is operated by a 1000W arc lamp power supply (ORIEL).The light from the arclamp is collected by a mirror and leaves the lamp housing through a condenser with a
diaphragm. A water filter is installed in front of the condenser to block the IR-light.
HCOCHO
HCOCHO
HCOCHO
HCOCHO
+ hn
+ hn
+ hn
+ hn




2 HCO
H2 + 2 CO
H2CO + CO
H + CO + HCO
DH°298
DH°298
DH°298
DH°298
= 68.5 kcal/mol,
= -2.1 kcal/mol;
= -1.7 kcal/mol;
= -85.4 kcal/mol;
lthreshold < 417 nm
all l
all l
lthreshold < 334 nm
Quantum chemical calculations
Adsorption of glyoxal and its possible photolytic products on water ice nanoparticles was
modelled using the water clusters (H2O)48, (H2O)72, (H2O)216, and (H2O)270. Among them the
largest one is the cluster corresponding the minimal nanoparticle size (n=275) to be
crystalline as observed experimentally. The clusters up to (H2O)72 were studied at the
B3LYP/6-31++G(d,p) and B3LYP/6-311++G(2d,2p) levels. The larger clusters were studied
using DFTBA and DFTB+ methods. Optimized structures, adsorption energies and
vibrational frequencies were obtained in the calculations.
Theoretical results
Experimental Results
Figure 1: Adsorption complexes of glyoxal and its UV photolysis products on the ice Ih
nanoparticles. BLYP/6-31++G(d,p) optimized structures.
Figure 3 below shows a section of the recorded FTIR spectra (difference spectra) of
glyoxal trapped in ice at 14K and the major photoproducts which are growing with incrasing
photolsyis time. For glyoxal CO, CO2 and HCHO were the main photoproducts observed
during the photodissociation studies at 14 K in in H2O-ice and also in a solid argon matrix.
0.20
Ice Ih nanoparticle
CO2
Difference spectra: before /after UV photolyis
0.15
10.5 А
+ Glyoxal
0.10
10 min
CO
HCOCHO
HCHO
5 min
0.00
+ hv (350 nm)
45 min
0.05
16.0 А
Absorbance
65 min
2400
2300
2200
2100
2000
1900
1800
1700
1600
-1
Wavenumber cm
Figure 3: FTIR difference spectra of glyoxal (HCOCHO) in H2O ice at 14K (before/after photolyis)
Table 1: Calculated energies and thermodynamic parameters of adsorption of glyoxal and
its photolytic products at the (0001) plane of (H2O)72 nanoparticle. B3LYP/6-31++G(d,p) and
B3LYP/6-311++G(2d,2p) (in parentheses) calculation results.
CO
HCHO
CO2
HCHO
Glyoxal
Figure 2: Ice nanoparticle (H2O)270 with 12 glyoxal molecules adsorbed at different
planes and sites. DFTB+ optimized structure. Left panel – top view; right panel – side
view. Calculated average energy of adsorption among 12 sites: –32.7 kJ/mol.
HCHO
Glyoxal
Figure 4: Difference spectra (before and after UV photolysis) of glyoxal isolated in a solid argon
matrix at 14K.
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Acknowledgements: SKI and OBG are thankful to AWI for the fellowship support. The work was supported
by the Eastpartnership program of DAAD and the Russian foundation for basic research (project No. 11-03-00085).