Hydrogenation processes from hydrogen peroxide: An investigation in Ne matrix for astrochemical purposes

Article abstract of DOI:10.1039/c4ra01920b

Hydrogenation processes are of paramount importance in the interstellar medium. Many laboratory experiments were carried out from unsaturated species. Herein, the hydrogenation of hydrogen peroxide was experimentally investigated step by step by means of the matrix isolation technique. This reaction leads to the formation of water. Moreover, the formation of H₃O₂ and OH radicals as intermediates was characterized. Such a hydrogenation process should take place on the surface of dust grains in the interstellar medium. This reaction is consistent with the very small amount of interstellar hydrogen peroxide. This hydrogenation process also takes place in solid phase. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra01920b

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Hydrogenation processes from hydrogen peroxide:
an investigation in Ne matrix for astrochemical
purposes
Cite this: RSC Adv., 2014, 4, 22172
ab
and Lahouari Krimab
*
Emilie-Laure Zins
Hydrogenation processes are of paramount importance in the interstellar medium. Many laboratory
experiments were carried out from unsaturated species. Herein, the hydrogenation of hydrogen peroxide
was experimentally investigated step by step by means of the matrix isolation technique. This reaction
leads to the formation of water. Moreover, the formation of H3O2 and OH radicals as intermediates was
characterized. Such a hydrogenation process should take place on the surface of dust grains in the
interstellar medium. This reaction is consistent with the very small amount of interstellar hydrogen
peroxide. This hydrogenation process also takes place in solid phase.
Received 5th March 2014
Accepted 7th May 2014
DOI: 10.1039/c4ra01920b
www.rsc.org/advances
OH + H / H2O
(2)
I. Introduction
This two-step mechanism was proposed by Watson & Sal-
pete,21 and its experimental feasability was demonstrated by
Dulieu et al.25 No activation energy is required for the reaction
Since the rst detection of a chemical species in the interstellar
medium in 1937,1,2 more than 160 compounds have been
characterized and identied in this dilute medium. In addition
to very simple molecules, such as CH4, NH3 and H2O, more
complex species are also present in these dilute media, such as
fullerenes, anthracene and metallic-containing molecules. It is
now well established that complex chemistry can occur in the
interstellar medium (ISM), and especially in molecular clouds,
on the surface of dust grains.3,4 As an example, numerous recent
studies have shown that hydrogenation reactions efficiently
take place in the ISM.5 Some of these reactions are listed in the
Table 1.
Most of the reactions above mentioned involve unsaturated
reagents. May such processes also occur from saturated
species? As far as the ISM is concerned, this question seems to
be particularly relevant in the case of hydrogen peroxide.
Indeed, water is one of the most widespread molecules in the
interstellar medium and the amount of water detected is much
greater than that predicted by all models. Many laboratory
experiments were carried out recently in order to identify and
understand the reaction pathways leading to the formation of
water in dense and diffuse molecular clouds.19 Three theoretical
models of formation of water in dense clouds have been
proposed over the last 30 years:20
(1), whereas the activation energy of the reaction (2) was esti-
mated at 22 kJ molꢁ1
.
27
The recombination of hydroxyl radicals may also be a source
of water on the surface of ice grains in the ISM.26–28
ꢀ a second pathway in 3 steps was proposed by Tielens &
Hagen in 1982:29
O + O2 / O3
(3)
(4)
(5)
O3 + H / O2 + OH
OH + H2 / H2O + H
Its experimental feasibility was demonstrated by Mokrane
et al.30
ꢀ a third pathway is also proposed by Tielens & Hagen in
1982 in 3 steps:32
O2 + H / HO2
HO2 + H / H2O2
(6)
(7)
(8)
H2O2 + H / H2O + OH
ꢀ a rst pathway consists of a successive hydrogenation of
oxygen:21–24
Reaction (6) is expected to take place without any activation
barrier,31 or with a very small activation energy (5.00 kJ molꢁ1 26
or 2.08 kJ molꢁ1 (ref. 32). No activation energy is associated to
O + H / OH
(1)
reaction (7).34
An activation energy of either 11.64 kJ molꢁ1
,
14.97 kJ
a
33
´
Sorbonne Universites, UPMC Univ Paris 06, UMR 8233, MONARIS, F-75005, Paris,
molꢁ1
,
or 17.15 kJ molꢁ1 (ref. 35) was determined for the
34
France. E-mail: emilie-laure.zins@upmc.fr
bCNRS, UMR 8233, MONARIS, F-75005, Paris, France
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Alternatively, Oba et al.38 investigated the possibility to form
water from a tunnelling effect in the reaction between OH
radicals and molecular hydrogen.39
Table
1 Examples of molecules that undergo hydrogenation
processes in the interstellar medium, that were experimentally
investigated
More precisely, the main laboratory's experiments on reac-
tions that may lead to the formation of water in the interstellar
medium are presented in Fig. 1.
Hydrogenation of
Reference
HNCO
HCN
CH2NH
CO2
Hudson et al.6
Theule et al.7
From this gure, we can conclude that peroxide hydrogen
can be formed without any activation energy, from HO2 or OH
radicals, and these two reactions are exothermic (ꢁ354 and
ꢁ211 kJ molꢁ1, respectively). Furthermore, the activation energy
associated to the formation of water from peroxide hydrogen is
very low (17 kJ molꢁ1) and can be easily overcome, even under
non-energetic conditions. Thus, the formation of water through
a reaction pathway involving peroxide hydrogen as an inter-
mediate appears to be an efficient process in the interstellar
medium.
Theule et al.7
Bisschop et al.8
CO
Fuchs et al.,9
Watanabe et al.,10 Pirim & Krim11
Oba et al.12
O
O2
Cuppen et al.,13 Miyauchi et al.,14
Chaabouni et al.,15 Lamberts et al.16
Mokrane et al.17
O3
NO
Fedoseev et al.18
Only recently was detected hydrogen peroxide in the inter-
stellar medium (ISM). Indeed, traces of H2O2 were only clearly
identied in 2011 by the APEX (Atacama Pathnder Experiment
telescope) telescope.41
In this work we will be interested mainly in the second
reaction of Tielens & Hagen32 and more particularly in the
third stage of the last reaction pathway, the hydrogenation
of a saturated bond. This reaction was theoretically investi-
gated by Koussa et al.39 Slightly different values were proposed
in the literature for this reaction. The main theoretically
values reported in the literature for the reactivity
between hydrogen peroxide and atomic hydrogen are reported
in Table 2.
reaction (8). Reaction (8) may play an important role in the ISM,
even if the amount of hydrogen peroxide present in these media
is limited. Indeed, Du and Parise have shown that this reaction
may explain the low abundance of H2O2 (a few percent in ices),
since hydrogen peroxide is constantly transformed into H2O by
reacting with the accreted H atoms.26,36 Furthermore, hydrogen
peroxide is considered to be an intermediate in the formation of
water, even in regions in which this molecule is under the
detection threshold.37
Miyauchi,14 Ioppolo19 like Oba12 proved the experimental
feasibility of this last reaction pathway. Each one of these ways
seems possible in the interstellar environments.
Fig. 1 Main reactions that may lead to the formation of water in the interstellar medium. For a sake of comparison of the activation energies and
the enthalpies change for the gas-phase reactions, all the initial states were put at zero. All these values were taken from Surface Processes on
Interstellar Amorphous Solid Water: Adsorption, Diffusion, Tunnelling Reactions, and Nuclear-Spin Conversion, Tetsuya Hama and Naoki
Watanabe, Chem. Rev., 2013, 113, 8783.40
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Table 2 Comparison of some theoretical data available in the literature for the reaction of hydrogen peroxide with either H or D atom
Paper
Reaction
Level of theory
Activation energy/DH (kJ molꢁ1
)
Reference
H2O2 + H / H2O + OH
H2O2 + H / H2 + HO2
H2O2 + H / H2O + OH
H2O2 + H / H2 + HO2
H2O2 + H / H2O + OH
H2O2 + D / HDO + OH
MP2//CASSCF/aug-cc-pVTZ
MP2//CASSCF/aug-cc-pVTZ
MPW1B95/M3G
+17.15/ꢁ284.9
+33.81/ꢁ63.13
+25.94/ꢁ297.90
+43.51/ꢁ68.62
+20.85/ꢁ281.43
+19.58/ꢁ289.03
Koussa et al. 2006 (ref. 35)
Tarchouna et al. 2006(ref. 42)
Ellingson et al. 2007 (ref. 43)
Ellingson et al. 2007 (ref. 45)
Taquet et al. 2012 (ref. 45)
Taquet et al. 2012 (ref. 45)
M05-2X/MG3S
GRAINOBLE astrochemical model44
GRAINOBLE astrochemical model
Hydrogen peroxide spontaneously leads to the formation of
➢ a reactivity study of a mixed water/hydrogen peroxide ice
water. In order to avoid a possible uncertainty between water with D/D2.
due to the decomposition of H2O2 and water molecules formed
A scheme of the experimental setup is presented in Fig. 2,
during the hydrogenation reaction, deuterium was used for this and the experimental method used for the present study has
study. Since it was not possible to work without water, we chose been described previously.46–48 The sample holder is a hexagonal
conditions in which water and hydrogen peroxide are formed in copper block on which rhodiated mirrors optically polished are
similar proportions, in order to reproduce the conditions of xed. This block is xed on the top of a cold head connected to a
astrochemical ices.
cryostat (Cryomech PT-405) operating with a circulating system
of liquid helium to the sample. The experimental setup was
optimized to be able to reach temperatures as low as 3 K on the
surfaces of the mirrors. The sample holder is set in an analysis
chamber that is connected to a microwave-driven atomic
source, an injection ramp, the infrared spectrometer and a
secondary pumping system.
II. Experimental technique
Two kinds of experiments were carried out:
➢ irradiations of hydrogen peroxide trapped in Ne matrix by
D/D2 at 10 K,
The chamber is maintained at a high vacuum of around 10ꢁ8
mbar thanks to a diffusion pump (Edwards, Standart Diffstack
160/700/P). The ramp gas, in stainless steel, is connected to a
pumping system (Edwards, Standart Diffstack 63/150M). This
ramp gas allows the preparation of gaseous mixtures with
piezoelectric gauges.
➢ and co-condensation of D/D2 and H2O2/Ne at 3 K.
For a sake of comparison, three additional experiments were
carried out:
➢ a reactivity study between hydrogen peroxide and molec-
ular D2,
➢ a reactivity study between water and D/D2,
Fig. 2 Scheme of the experimental setup used for the present study.49
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Deuterium atoms were generated from molecular deuterium infrared (FTIR) spectrometer. Bare mirror backgrounds, recor-
(Sigma Aldrich), by a microwave-driven atomic source (SPECS, ded from 4500 to 500 cmꢁ1 prior to sample deposition, were
PCS-ECR), whose operation is briey described herein.
used as references in processing the sample spectra. A KBr
Inside the plasma chamber, electron cyclotron resonance window is mounted on a rotatable ange separating the inter-
method is used to achieve massive dissociation of molecules in ferometer vacuum (10ꢁ3 mbar) from that of the cryostatic cell
the plasma. Our ECR (electron cyclotron resonance) atomic (10ꢁ7 mbar). The signal is then directed to a MCT (HgCdTe)
source has a specially designed aperture which inhibits the detector. All spectra were recorded at 3 K.
release of ions from the plasma while allowing neutral atoms
The attributions are based on the previous published
and molecules to effuse out. The particles released are largely works.53,54,54,55,55,56
thermalized, with an atom ux of about 1017 atoms per cmꢁ3
per second. 1 bar of D2 is introduced inside the microwave-
driven atomic source and the pressure of the chamber during
operation of the atom source is 10ꢁ5 mbar. The gas leaving the
III. Results
Before presenting our experimental results on the reactivity
chamber through the apertures is a combination of both atomic
and molecular deuterium D/D2 (15/85).
The ramp gas also allows the introduction of Ne gas inside a
round-bottom ask containing the hydrogen peroxide adsorbed
on urea.
between H2O2 and D atoms, we would like to comment refer-
ence experiments that were needed to ascertain the processes
described below. Indeed, since the efficiency of the microwave-
driven atomic-source, molecular D2 was introduced in the
chamber concomitantly with atomic D. This is the reason why
we carried out experiments in which microwave-driven atomic-
source was switched off. Under such experiments, similar
spectra than the ones obtained when H2O2/Ne was condensed
alone, were obtained. Thus, without any surprise, hydrogen
peroxide do not react with molecular deuterium, and the
phenomena described below are indeed due to the reaction
between hydrogen peroxide and atomic deuterium.
In the context of laboratory experiments for astrochemically-
relevant studies, hydrogen peroxide was extensively studied in
rare gas matrix,50–52 and a similar approach was used for the
present study.
H2O2 adsorbed on urea (Sigma-Aldrich) was used. This solid
powder was introduced in a round bottom ask. Under our
experimental conditions, it appears that the best way to
condense hydrogen peroxide without destroying it is achieved
when the round bottom ask is heated at around 50–60 ꢂC
(Fig. 3). The gaseous mixture is then carried inside the reaction
chamber thanks to a neon ux. These conditions lead to the
formation of a neon matrix in which a large amount of hydrogen
peroxide, as well as water are trapped.
a. Irradiation of H2O2/Ne by D/D2 at 10 K
First, H2O2/Ne was condensed at 3 K on the surface of the
mirror, and this sample was further heated up to 10 K and
subjected to a D/D2 beam. This bombardment was carried out at
10 K to avoid the condensation of molecular deuterium on the
surface of the sample. Spectra were registered before the D/D2
exposure and during the exposure every 5 minutes, during 40
minutes. Fig. 4 shows the spectra obtained. The spectrum of the
initial sample containing hydrogen peroxide in Ne matrix is
shown, as well as difference spectra between this spectrum and
the ones obtained aer the exposures.
Infrared absorption spectra of the samples obtained by
condensation of gaseous mixtures were recorded in the trans-
mission-reection mode between 4500 and 500 cmꢁ1 with a
resolution of 0.5 cmꢁ1 using a Bruker 120 Fourier transform
The disappearance of H2O2 and H2O2 dimer are observed,
with the concomitant formation of H2O, HDO and D2O (Fig. 4).
Until 40 min. of reaction, this behavior is observed. Further-
more, the formation of D2O2 is observed when the initial H2O2
sample is bombarded during 5 to 25 min. with a D/D2 beam.
Aer 25 minutes, the amount of D2O2 strongly decreases. Wide
bands centered at 2650, 2525 and 2420 cmꢁ1, signature of
dangling HDO/D2O, are formed during the exposure of H2O2 in
Ne matrix to a D/D2 beam. The structure at 2650 cmꢁ1 may be
due to (D2O)2, (HDO)2 or OD radicals interacting with a water
ice. The formation of such an ice, even aer short exposure
times, from matrix isolated samples, suggests that exothermic
reactions take place.
b. Co-condensation of D/D2 and H2O2/Ne at 3 K
These results clearly show that hydrogen peroxide can react
with atomic deuterium to form water molecules. However, in
this series of experiments that was carried out at 10 K, the
reaction quickly leads to the formation of a water ice, whereas
Fig. 3 Main IR bands of H2O2 observed in Ne matrix from H2O2
adsorbed on urea, depending of the heating of the round flask con-
taining the reagent. Except mentioned otherwise, all the attributions
are related to H2O2.
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Fig. 4 IR spectrum of the initial H2O2 sample in Ne matrix (in bold), and difference spectra after exposure to a D/D2 beam during 5 to 40 min. In
the H2O2 bending region of hydrogen peroxide (top, left). In the n2 bending region of D2O (top, right). In the OD stretching regions of D2O and
HDO ices (bottom, left). A wide band centred at 2420 cmꢁ1 is observed, as well as two structures at 2650 and 2525 cmꢁ11, in the D2O2 bending
region (bottom, right).
we were interested in a step-by-step study. This is the reason species. When this sample is maintained in the dark at 3 K
why we carried out a second reactivity study in Ne matrix, at 3 K. during 160 min, no dramatic change is observed. This result
In this series of experiments, H2O2/Ne and D/D2 were simulta- clearly indicates that a tunneling effect is involved in the reac-
neously condensed on the surface of the cold mirror. This leads tions that lead to the formation of water from H2O2 and D.
to the formation of a sample containing H2O2/D trapped inside a
When the sample is further annealed up to 9 K, the amount
D2/Ne matrix. Since preliminary experiments have shown that of H2O2 is still decreasing, and an additional formation of HDO
molecular deuterium is inert toward hydrogen peroxide, the and D2O is observed.
presence of D2 does not affect our experiments. The main species
The band at 1021 cmꢁ1 corresponds to OD2 species. This
introduced during the condensation of the samples is Ne. As a species has also a characteristic band at 2529 cmꢁ1. These
consequence, we can consider that the samples are obtained in bands are observed in the sample obtained aer the co-
Ne matrix, and the presence of molecular D2 can be neglected.
condensation of hydrogen peroxide and D atoms in Ne matrix.
In order to further gain some insight on the reaction Then they both decrease during the annealing of the sample.
processes, dark reactions and annealing experiments were carried This evolution suggests that the DO2 radical initially formed,
out. In the former experiments, the sample was maintained at 3 K further react with D atoms through tunneling effect.
without any radiation. These experiments allow to follow reac-
Two other bands at 1028 and 1033 cmꢁ1 are assigned to the
tions that do not require energy to take place. Typically, tunneling OD symmetric bending of D2O2. These bands are observed in
effects can be observed in such experiments. To further allow the sample obtained aer the co-condensation of hydrogen
reagents to react in the neon matrix, the sample was annealed, peroxide and D atoms in Ne matrix. The intensities of these
thus increasing the diffusion of the species in the matrix.
bands are almost constant during the dark reaction and slightly
Fig. 5 shows the spectra obtained aer the co-condensation decrease aer the sample annealing.
of hydrogen peroxide and atomic deuterium, as well as the
inuence of a dark reaction (160 min) and an annealing (up to
9 K), in the OH/OD bending and stretching spectral regions.
c. Co-condensation of D/D2 and H2O/Ne at 3 K
Hydrogen peroxide as well as HDO and D2O are present in
the sample obtained just aer the co-condensation of the
The aim of this experiment was to verify that the formation of
HDO and D2O previously observed is not only due to a
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Fig. 5 Co-condensation of hydrogen peroxide and atomic deuterium in a Ne matrix. Initial spectrum (in bold), and Spectra registered after a dark
reaction of 160 min (solid line) and after an annealing at 9 K (dotted line). Left: Bending spectral regions of HDO, D2O and H2O2. Right: Spectral
regions of O–D stretching of DO2 (expected at 2549 cmꢁ1 in the gas phase), O–D symmetric bending of D2O2 (1029 cmꢁ1 in the gas phase),
bending of DO2 (1020 cmꢁ1 in the gas phase).
hydrogen/deuterium transfer from water molecules (due to cryogenic mirror maintained at 10 K, and then further exposed
partial decomposition of hydrogen peroxide). Fig. 6 clearly to the D/D2 beam. The spectra obtained before and aer the
shows that, under the same conditions as the ones used for the exposure are shown in Fig. 8. Based on the results above pre-
previous experiment, H2O is almost unreactive toward atomic sented and obtained in neon matrix, it is possible to analyze
deuterium. Indeed, only a very small amount of HDO and D2O is these spectra registered in solid phase. A structural change in
observed aer the co-condensation of H2O/Ne and D/D2 at 3 K. the wide band centered at 3200 cmꢁ1 concomitantly with the
Thus, the formation of HDO, D2O, D2O2 and DO2 previously disappearance of the band around 2820 cmꢁ1. Furthermore, the
observed, was due to the reaction between hydrogen peroxide formation of a water ice is observed. It appears that the formation
and atomic deuterium.
of water from hydrogen peroxide that was previously observed in
neon matrix takes place in the same way in solid phase.
d. Irradiation of a H2O2 ice by D/D2 at 10 K
IV. Discussion
A further question was to know whether such a reaction leading
to the formation of water from hydrogen peroxide, can also take
place in solid phase. Indeed, this point is of primary relevance
in the context of chemistry that may take place on the surface of
ice grains in the interstellar medium. To determine whether a
similar reaction takes place in solid phase, or if other processes
occur, hydrogen peroxide was deposited on the surface of the
The results presented below clearly show that, as proposed in
the literature, hydrogen peroxide can react with atomic
hydrogen to form water, even in neon matrix, at a temperature
as low as 3 K, from reagents in their fundamental state. Thus, if
hydrogen peroxide is formed in the interstellar medium, it may
react spontaneously with atomic hydrogen to form water
molecules. This may explain, at least partially, why hydrogen
peroxide is not present in abundant proportions in the inter-
stellar medium.
This is consistent with what we expected. Indeed, the
reaction
H2O2 + D / HDO + OH
(9)
is expected to have an activation barrier of about +19.58 kJ
molꢁ1
.
49
Thus, under our non-energetic conditions, this reaction is
not supposed to take place. However, two hypotheses can be
proposed to explain the reactivity observed:
(i) either the reaction (9) proceeds via a quantum tunneling
process,
Fig. 6 Co-condensation of water and atomic deuterium in a Ne matrix
(dotted line). For a sake of comparison, the spectrum obtained after a
co-condensation of hydrogen peroxide and atomic deuterium in a Ne
matrix is also shown. The absorbances of the two spectra are
normalized.
-(ii) or the exothermicity of the reaction favors further reac-
tions aer a rst initial and slow process.
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(i) Let us rst consider the occurrence of quantum tunneling theoretically.63 H-atom tunneling may also be involved in the
process under our experimental conditions. Quantum hydrogenation processes of CO, leading to the formation of
tunneling processes may play a fundamental role in the chem- methanol,64,65 as well as in the isomerization processes of small
ical processes occurring on the surface of dust grains in radicals.66 As far as reactions involving the formation of water
molecular clouds.56–58 As an example, it was proposed that O and/or hydrogen peroxide, quantum tunneling processes may
atoms can diffuse by quantum mechanical tunneling.59 Such a also be involved.14,44,67,68 If a quantum tunneling process
tunneling can lead to the formation of interstellar CO2 on the occurred under our experimental conditions, a reaction would
surface of dust grains, from CO molecules.60,61 The importance have been observed during experiments in the dark (Fig. 5), as it
of tunneling in the formation of molecular hydrogen on inter- was in the case of reaction between hydrogen atoms and carbon
stellar grains was also investigated, both experimentally62 and monoxide69 for instance. This result suggests that the reaction
observed under our experimental conditions is not governed
only by a quantum tunneling mechanism.
(ii) To the best of our knowledge of the literature, the effect of
exothermicity in reactions that take place on interstellar grains
was taken into account only recently. Until then, it was
considered that the grain surface processes are memoryless.
However, a new kinetic Monte Carlo model that takes into
account a non-Markovian behavior of species formed during an
exothermic reaction was proposed.70 The simulations that were
carried out with this model have shown that the exothermicity
may play a fundamental role in some cases, such as the reaction
between H and HO2.70
Under our experimental conditions, the exothermicity is
clearly of primary importance in the reactivity observed. Indeed,
Fig. 7 Irradiation of a H2O2 ice by a D/D2 beam. The disappearance of
the quick formation of water ices during the exposure of a H2O2/
H2O2 with the concomitant formation of a water ice is observed. The
Ne sample to D atoms is clearly due to an exothermic process.
star indicates a small amount of water present in the initial sample
Additionally, the formation of D2O DO2 and D2O2 suggests that
because of a natural decomposition of hydrogen peroxide molecules.
Fig. 8 Main reactions proposed to explain the formation of the different products observed during the reaction between hydrogen peroxide and
atomic deuterium (see the text). Solid lines correspond to hydrogenation processes, whereas dotted lines correspond to de-hydrogenation
processes. For each reaction, the activation energy as well as the enthalpies of the reaction in the gas phase are indicated in kJ molꢁ1, according
to the literature. (A) see ref. 43; (B) see ref. 45; (C) see ref. 58. When the values quoted correspond to a similar process involving non-deuteriated
species, a star was added.
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the products observed during these experiments are not only
due to the reaction (9). A more complex process should be
involved.
2 W. S. Adams, Astrophys. J., 1941, 93, 11.
3 E. F. van Dishoeck, E. Herbst and D. A. Neufeld, Chem. Rev.,
2013, 113, 9043.
The reaction (9) corresponds to a very exothermic process
(DH ¼ ꢁ289.03 kJ molꢁ1).49 If one hydrogen peroxide molecule
reacts with one atomic deuterium to form a water molecule and
an hydroxy radical, a large amount of energy will be released. As
a consequence, the products of the reaction will be able to
diffuse a little bit in the sample (even in a neon matrix), such as
(10) and (11).
4 C. J. Bennett, C. Pirim and T. M. Orlando, Chem. Rev., 2013,
113, 9086.
5 S. Ioppolo, H. M. Cuppen and H. Linnartz, Rend. Fis. Acc.
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9 G. W. Fuchs, H. M. Cuppen, S. Ioppolo, C. Romanzin,
S. E. Bisschop, S. Andersson, E. F. van Dishoeck and
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OH + D / HDO
(10)
(11)
OH + D2 / HDO + D
Furthermore, another reaction between hydrogen peroxide
and atomic hydrogen may lead to the formation of hydroperoxy
radical (reaction (12)):
H2O2 + H / H2 + HO2
(12)
The activation energy associated to this exothermic reaction
(ꢁ63.13–68.62 kJ molꢁ1
)
is rather high (+33.81 kJ molꢁ1 or
46,47
+43.51 kJ molꢁ1).46,47 Thus, under our experimental conditions,
this reaction can proceed either via a quantum tunneling
mechanism, or from hot species.
13 H. M. Cuppen, S. Ioppolo, C. Romanzin and H. Linnartz,
Phys. Chem. Chem. Phys., 2010, 12, 12077.
14 N. Miyauchi, H. Hidaka, T. Chigai, A. Nagaoka, N. Watanabe
and A. Kouchi, Chem. Phys. Lett., 2008, 456, 27.
The exothermicity of the reaction (9), in combination with
quantum tunneling mechanism, and in combination with
reactions due to the diffusion of species, may explain the
various species observed under our experimental conditions. As
an example, a scheme of consecutive process that may take
place is proposed in Fig. 7.
`
15 H. Chaabouni, M. Minissale, G. Manico, E. Congiu,
J. A. Noble, S. Baouche, M. Accolla, J. L. Lemaire,
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234706.
16 T. Lamberts, H. M. Cuppen, S. Ioppolo and H. Linnartz,
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18 G. Fedoseev, S. Ioppolo, T. Lamberts, J. F. Zhen,
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20 R. G. Smith, S. B. Charnley, Y. J. Pendleton, C. M.Wright,
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V. Conclusion
The conversion of hydrogen peroxide to water in the interstellar
medium may explain the relative abundances of these two
species in dense and molecular clouds. To investigate this
point, we carried out experiments in neon matrix in order to
follow the hydrogenation of hydrogen peroxide step by step,
using atomic deuterium. The formation of mixed D2O/HDO2/
H2O2/D2O2 ices, demonstrates that the hydrogenation of
hydrogen peroxide is indeed an efficient way to produce water.
Furthermore, our results clearly show that this hydrogenation
reaction is exothermic.
21 W. D. Watson and E. E. Salpeter, Astrophys. J., 1972, 174(321),
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In order to further characterize this hydrogenation reaction,
experiments in which H2O2/Ne was co-condensed with atomic
deuterium, were carried out. The initial formation of water
molecules suggest that almost no activation energy is needed
for this reaction. A progressive reaction is observed during the
dark reaction, as a consequence of the diffusion of deuterium
atoms. These results are in total agreement with the theoretical
data (activation energy and enthalpy of formation) known for
the H2O2/H reaction.
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