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 RI05: 02:38 PM – 02:53 PM RI. MATRIX ISOLATION (AND DROPLETS) 

Reaction of atomic hydrogen with formic acid # Kr matrix T/K H + HCOOH → trans-H 2 COOH trans-H 2 COOH → trans-cis-HC(OH) 2 # Q. Cao, S. Berski, Z. Latajka, M. Räsänen, and L. Khriachtchev, PCCP 16, 5993 (2014). HCOOH/HBr/Kr (1/2/1000) 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

Solid parahydrogen (para-H 2 ) matrix isolation T/K pH 2 matrix H + DCOOD → HD + trans-DOCO nm photolysis at 1.9 K, generate H-atoms 2. H-atoms mobile, record repeated FTIR scans J=0 pH 2 HCOOH/pH 2 (1/10,000) HCOOH + h → CO + D 2 O → CO 2 + D 2 K. Kufeld, W. Wonderly, L. Paulson, S. Kettwich, and DTA, JPC Lett. 3, (2012). W. Wonderly and DTA, Low Temp. Phys. 38, 853–859 (2012). HDO + H + pH 2 reaction with pH 2 host → DCO + OD

H+DCOOD in pH 2 at 1.9 K: Experimental protocol atmosphere vacuum FTIR beam radiation shield optical substrate pH 2 crystal pre-cooled pH 2 gas dopant gas UV beam M.E. Fajardo and S. Tam, J. Chem. Phys. 108, (1998). Deposit crystal at <2.5 K (rapid vapor deposition) Photolyze sample (193 nm, 85  J cm -2 sec -1 ) Repeated FTIR scans (5 min acquisition times, at 0.03 cm -1 resolution) Liquid helium bath cryostat

Infrared spectroscopy of DCOOD 1 (O-D stretch) K.L. Goh, P.P. Ong, H.H. Teo, and T.L. Tan Spectrochimica Acta A 59, 1773 (2000). 3 (C=O stretch) F. Madeja, A. Hecker, S. Ebbinghaus, M. Havernith Spectrochimica Acta A 59, 1773 (2003). 4 (C-O stretch) 5 (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 pH 2 Frequencies agree well with literature values Isotopic scrambling leads to some production of DCOOH and HCOOD Fermi

193 nm photolysis of DCOOD/pH 2 As-deposited, 1.9 K 193 nm photolysis, 7.2 min, 1.9 K (32% reduction in DCOOD) 9.5 hrs, dark, 1.9 K Experimental conditions [DCOOD]=57, [DCOOH]=8, [HCOOD]=2, [HCOOH]=0.5 ppm 2.5(1) mm thick

H + DCOOD reactions after photolysis As-deposited, 1.9 K 193 nm photolysis, 7.2 min, 1.9 K (32% reduction in DCOOD) 9.5 hrs, dark, 1.9 K HCO clusters C=O stretch region

Identifying and assigning trans-DOCO D O O C Daniel Forney, Marilyn E. Jacox, and Warren E. Thompson, “Infrared spectra of trans-HOCO, HCOOH +, and HCO 2 - trapped in solid neon,” J. Chem. Phys. 119, (2003). trans-DOCO

Matrix shifts: Observed trends modegastheory*NepH 2 Ar t-HOCO 1 O-H stretch (5.3) (-7.7) (-23.5)3602.9(-32.8) 2 C=O stretch (9.4) (-4.6) (-7.5)1843.6(-9.0) 3 H-O-C bend C-O stretch t-DOCO 1 O-D stretch (1.0)2678.1(-6.0) (-16.9) 2 C=O stretch (8.2)1846.2(-5.4) (-8.4)1841.7(-9.9) 3 D-O-C bend C-O stretch Table 1. Vibrational frequencies (matrix shifts) in cm -1 for t-HOCO and t-DOCO. *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, (2013).

In situ photochemistry: HCOOH → products h -18 ppm +18 ppm +1 ppm +8 ppm +17 ppm +19 ppm+25 ppm DCOOD + h → CO + D 2 O DCOOD + h → DCO + OD D + COH + HDO h + pH 2 DCOOD + h → D 2 + CO 2 significant channel (30%) minor channel (5%) major channel (65%) photo DCOOD decrease approximately matches total product increase

H-atom diffuses via “chemical” tunneling H + H 2 → H 2 + H E a = 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, (2003).

DOCO Diffusion limited tunneling reaction H + DCOOD → HD + DOCO E a = 9.5(3) kcal/mol A.M. Lossack, D.M. Bartels, E. Roduner, Res. Chem. Intermed. 27, (2001). = 3330(100) cm -1 DCOOD H H H+DCOOD HD+DOCO HD

Anomalous temperature dependence photo 1 photo 2 No reactions!

Deuterium substitution supports reaction scheme H+DCOOD → HD + DOCOH+HCOOH → H 2 + HOCO reaction with C-atom of formic acid

Kinetics change abruptly with temperature!

Very small kinetic isotopic effect (KIE) k HOCO = 5.39(5)x10 -3 min -1 k DOCO = 3.44(6)x10 -3 min -1 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 pH 2 Anomalous temperature effects 1. H-atom mobility 2. Chemical reactivity H+DCOOD → HD+DOCO 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 pH 2 at 1.9 K

The people who do the work and funding William R. Wonderly 2011 REU Now UCSB Graduate Student This research was sponsored in part by the Chemistry Division of the US National Science Foundation (CHE ). Fredrick M. Mutunga 2 nd year UW Graduate Student Shelby E. Follett 1 st year UW Graduate Student