Energy-Resolved Collision-Induced Dissociation of Peroxyformate
Anion: Enthalpies of Formation of Peroxyformic Acid and
Peroxyformyl Radical
Alex A. Nickel, Jerry G. Lanorio, and Kent M. Ervin*
Department of Chemistry, University of Nevada, Reno, 1664 North Virginia Street MS 216, Reno, Nevada 89557-0216, United States
* S Supporting Information
ABSTRACT: We measure the oxygen-oxygen bond dissoci-
ation energy of the peroxyformate anion (HCO
3
-
) using
energy-resolved collision-induced dissociation with a guided
ion beam tandem mass spectrometer. The analysis of the
dissociation process from HCO
3
-
(
1
A′) to HCO
2
-
(
1
A
2
)+
O(
3
P) requires consideration of the singlet-triplet crossing
along the reaction path and of the competing OH
-
and O
2
H
-
product channels. The measured oxygen-oxygen bond
dissociation energy is D
0
(HCO
2
-
-O) = 1.30 ± 0.13 eV
(126 ± 12 kJ/mol). This threshold energy measurement is
used in thermochemical cycles to derive the enthalpies of formation for peroxyformic acid, Δ
f
H
0
(HCO
3
H) = -287 ± 19 kJ/mol,
and peroxyformyl radical, Δ
f
H
0
(HCO
3
•
)= -98 ± 12 kJ/mol. These values are in good agreement with computational energies.
■
INTRODUCTION
The formyl radical, HCO
•
, is a reaction intermediate observed
in the combustion of a variety of hydrocarbon species.
1
Once
formed, the formyl radical will undergo an oxidation reaction,
eq 1.
2-10
+ → → +
• • •
HCO O [HCO ] HO CO
2 3 2
(1)
This reaction is a major source of hydroperoxy radicals, HO
2
•
,
which play a role in the formation of photochemical smog from
volatile organic compounds.
11,12
The HCO
•
+O
2
reaction can
also produce HO
•
+ CO
2
products or, at high pressures, the
stabilized peroxyformyl radical.
3,4,9
Experimental evidence and
theoretical calculations imply that the reaction intermediate for
reaction 1 is a peroxyformyl radical.
2,3,6-10
Matrix-isolation
infrared spectroscopic measurements of photolyzed form-
aldehyde, H
2
CO, in the presence of O
2
show vibrational
frequencies assigned to the peroxyformyl radical.
7,13
There has
been some debate as to whether the radical intermediate is
sufficiently vibrationally excited to dissociate directly or
whether the peroxyformyl radical (HCOO
2
•
) passes through
the hydroperoxooxomethyl radical complex (HOOC
•
O).
8,9
The thermochemistry of peroxyformic acid and the
peroxyformyl radical is not yet experimentally established and
is addressed in this work using ion chemistry techniques. The
negative ion thermochemical cycles
14
for formic acid (HCO
2
H)
and peroxyformic acid (HCO
3
H) are shown in Figure 1. The
negative ion thermochemical cycle, eq 2, relates the gas-phase
acidity of the acid RH and the electron affinity of the radical R
•
to the bond dissociation energy of RH.
− =Δ + −
•
D H (R H) (RH) EA(R ) IE(H)
acid
(2)
For formic acid, shown on the left-hand side of Figure 1, these
values as well as the enthalpies of formation of formic acid and
formyl radical (HCO
2
•
) are fairly well established experimen-
tally.
15-17
Recent experiments by Villano et al.
10
provide the
energetics of the negative ion thermochemistry cycle for
peroxyformic acid (HCO
3
H), shown on the right-hand side of
Figure 1. Villano et al.
10
carried out negative ion photoelectron
spectroscopy measurements to determine the electron affinity
of the peroxyformyl radical (HCO
3
•
) and flowing-afterglow
selected-ion flow tube measurements to determine the gas-
phase acidity of peroxyformic acid. That provides the O-H
bond dissociation energy of peroxyformic acid,
10
D(HCO
3
-
H), via eq 2. However, because the enthalpy of formation of the
parent peroxyformic acid is not known experimentally, neither
is the enthalpy of formation of the peroxyformyl radical. Villano
et al.
10
further observed that the peroxyformate anion
undergoes collision-induced dissociation to form the formate
anion (HCO
2
-
) and an oxygen atom in the ion injection region
of their flow tube. In this work, we examine the threshold
collision-induced dissociation (TCID) of the peroxyformate
anion, eq 3
+ → + +
− −
HCO Xe HCO O Xe
3 2
(3)
where xenon is the target gas, in an energy-resolved fashion
using guided ion beam tandem mass spectrometry. In the
absence of a reverse activation energy, an assumption addressed
Special Issue: Peter B. Armentrout Festschrift
Received: March 2, 2012
Revised: April 4, 2012
Published: April 5, 2012
Article
pubs.acs.org/JPCA
© 2012 American Chemical Society 1021 dx.doi.org/10.1021/jp302089q | J. Phys. Chem. A 2013, 117, 1021-1029