Y
RI05: FTIR STUDIES OF THE
PHOTOCHEMISTRY OF
DEUTERATED FORMIC ACID
IN A PARAHYDROGEN MATRIX
David T. Anderson
Department of Chemistry, University of Wyoming
Laramie, WY 82071-3838
danderso@uwyo.edu
RI05: 02:38 PM – 02:53 PM
RI. MATRIX ISOLATION (AND DROPLETS)
Reaction of atomic hydrogen with formic acid#
Kr matrix
T/K
30
20
10
0
HCOOH/HBr/Kr (1/2/1000)
1. 193 nm photolysis at 4.3 K
2. Anneal at 31 K, induce H-atom mobility
3. Re-cool to 4.3 K and record FTIR scans
#Q.
H + HCOOH → trans-H2COOH
trans-H2COOH → trans-cis-HC(OH)2
Cao, S. Berski, Z. Latajka, M. Räsänen, and L. Khriachtchev, PCCP 16, 5993 (2014).
Solid parahydrogen (para-H2) matrix isolation
pH2 matrix
HCOOH + hn → CO + D2O
→ CO2 + D2
→ DCO + OD
+ pH2
T/K
30
20
10
0
pH2
HDO + H
reaction with
pH2 host
J=0
HCOOH/pH2 (1/10,000)
H + DCOOD → HD + trans-DOCO
1. 193 nm photolysis at 1.9 K, generate H-atoms
2. H-atoms mobile, record repeated FTIR scans
K. Kufeld, W. Wonderly, L. Paulson, S. Kettwich, and DTA, JPC Lett. 3, 342-347 (2012).
W. Wonderly and DTA, Low Temp. Phys. 38, 853–859 (2012).
H+DCOOD in pH2 at 1.9 K: Experimental protocol
Liquid helium bath cryostat
UV
beam
atmosphere
vacuum
pH2
crystal
dopant
gas
Deposit crystal at <2.5 K
(rapid vapor deposition)
Photolyze sample
(193 nm, 85 mJ cm-2 sec-1)
FTIR
beam
radiation
shield
Repeated FTIR scans
(5 min acquisition times,
at 0.03 cm-1 resolution)
optical
substrate
pre-cooled
pH2 gas
M.E. Fajardo and S. Tam, J. Chem. Phys. 108, 4237-4241 (1998).
Infrared spectroscopy of DCOOD
n3 (C=O stretch)
F. Madeja, A. Hecker, S. Ebbinghaus, M. Havernith
Spectrochimica Acta A 59, 1773 (2003).
n1 (O-D stretch)
K.L. Goh, P.P. Ong, H.H. Teo, and T.L. Tan
Spectrochimica Acta A 59, 1773 (2000).
n4 (C-O stretch)
n5 (C-O bend)
T.L. Tam, K.L. Goh, P.P. Ong, H.H. Teo
J. Mol. Spectrosc. 195, 324 (1999).
Infrared spectroscopy of DCOOD in solid pH2
Fermi
• Frequencies agree well with literature values
• Isotopic scrambling leads to some
production of DCOOH and HCOOD
193 nm photolysis of DCOOD/pH2
Experimental conditions
[DCOOD]=57, [DCOOH]=8,
[HCOOD]=2, [HCOOH]=0.5 ppm
2.5(1) mm thick
9.5 hrs, dark, 1.9 K
193 nm photolysis, 7.2 min, 1.9 K
(32% reduction in DCOOD)
As-deposited, 1.9 K
H + DCOOD reactions after photolysis
C=O stretch region
HCO clusters
9.5 hrs, dark, 1.9 K
193 nm photolysis, 7.2 min, 1.9 K
(32% reduction in DCOOD)
As-deposited, 1.9 K
Identifying and assigning trans-DOCO
D
C
O
trans-DOCO
O
Daniel Forney, Marilyn E. Jacox, and Warren E. Thompson,
“Infrared spectra of trans-HOCO, HCOOH+, and HCO2trapped in solid neon,” J. Chem. Phys. 119, 10814-10823
(2003).
Matrix shifts: Observed trends
Table 1. Vibrational frequencies (matrix shifts) in cm-1 for t-HOCO and t-DOCO.
mode
t-HOCO
t-DOCO
gas
theory*
Ne
pH2
Ar
n1 O-H stretch
3635.70
3641.0(5.3)
3628.0(-7.7)
3612.20(-23.5)
3602.9(-32.8)
n2 C=O stretch
1852.57
1862.0(9.4)
1848.0(-4.6)
1845.08(-7.5)
1843.6(-9.0)
n3 H-O-C bend
1212.7
1210.4
1210.27
1211.2
n4 C-O stretch
1052.0
1050.4
1064.6
n1 O-D stretch
2684.11
2685.1(1.0)
2678.1(-6.0)
2667.26(-16.9)
n2 C=O stretch
1851.64
1859.8(8.2)
1846.2(-5.4)
1843.26(-8.4)
1841.7(-9.9)
n3 D-O-C bend
1086.4
1082.6
1086.44
1092.6
n4 C-O stretch
902.6
*X. Huang, R.C. Fortenberry, Y. Wang, J.S. Francisco, T.D. Crawford, J.M. Bowman, T.J. Lee, “Dipole Surface and Infrared
Intensities for the cis- and trans-HOCO and DOCO Radicals,” J. Phys. Chem A. 117, 6932-6939 (2013).
hn
In situ photochemistry: HCOOH → products
DCOOD + hn → CO + D2O
significant channel (30%)
DCOOD + hn → D2 + CO2
minor channel (5%)
DCOOD + hn → DCO + OD
major channel (65%)
hn
+ pH2
D + CO H + HDO
-18 ppm
+19 ppm
+25 ppm
photo
+18 ppm
+17 ppm
+1 ppm
+8 ppm
• DCOOD decrease approximately matches total product increase
H-atom diffuses via “chemical” tunneling
H + H2 → H2 + H
Ea = 10 kcal/mol
= 3500 cm-1
T. Kumada, “Experimental determination of the mechanism of the tunneling diffusion of
H-atoms in solid hydrogen: Physical exchange versus chemical reaction,” Phys. Rev. B
68, 052301 (2003).
Diffusion limited tunneling reaction
H + DCOOD → HD + DOCO Ea = 9.5(3) kcal/mol
= 3330(100) cm-1
HD
DCOOD
DOCO
H
DCOOD
H H+DCOOD
HD+DOCO
A.M. Lossack, D.M. Bartels, E. Roduner, Res. Chem. Intermed. 27, 475-483 (2001).
Anomalous temperature dependence
No reactions!
photo 1
photo 2
Deuterium substitution supports reaction scheme
H+DCOOD → HD + DOCO
• reaction with C-atom of formic acid
H+HCOOH → H2 + HOCO
Kinetics change abruptly with temperature!
Very small kinetic isotopic effect (KIE)
kHOCO = 5.39(5)x10-3 min-1
kDOCO = 3.44(6)x10-3 min-1
KIE 
k HOCO
 1.57
k DOCO
rate-determining step
(rds) is not tunneling,
i.e., diffusion limited
secondary KIE, no
bond to the D-atom is
broken in the rds
Low-temperature H-atom chemistry in solid pH2
H+DCOOD → HD+DOCO
Anomalous temperature effects
1. H-atom mobility
2. Chemical reactivity
Tunneling Reactions of H-atoms with Formic Acid and Carbon
Monoxide in Solid Parahydrogen I: Anomalous Temperature Effects
Tunneling Reactions of H-atoms with Formic Acid and Carbon
Monoxide in Solid Parahydrogen II: Deuterated Reaction Studies
Submitted to J. Phys. Chem. A, under revision (2014).
Summary
Assign IR features to trans-DOCO
Isotopic substitution reveals reactive partner is DCOOD and reacts
at C-atom
Chemical kinetics change abruptly at ~2.7 K
· transition to “controlled” chemistry
· quantum solvent effects
Reaction of hydrogen atoms with formic acid leads to qualitatively
different products in Kr at 31 K compared to pH2 at 1.9 K
The people who do the work and funding
William R. Wonderly
2011 REU
Now UCSB Graduate Student
Fredrick M. Mutunga
2nd year
UW Graduate Student
Shelby E. Follett
1st year
UW Graduate Student
This research was sponsored in part by the Chemistry Division
of the US National Science Foundation (CHE 08-48330).