Investigation of the Amide I Band of N-Methylacetamide in Solid Parahydrogen using FTIR Spectroscopy Leif O. Paulson and David T. Anderson Department of Chemistry University of Wyoming, Laramie, WY Monday, June 22, 2009

Overview N-Methylacetamide Experimental setup Examination and discussion of the Amide I feature Summary

N-Methylacetamide (NMA) H H H H trans-N-Methylacetamide

NMA IR Transition 1 FWHM = 4.5 cm L. O. Paulson and D. T. Anderson. 61 st Ohio State University International Symposium on Molecular Spectroscopy, talk R008 (2006)

Why NMA? Amide I Vibrational Mode Simple model of peptide bond Well studied specimen Amide I mode is extremely sensitive to its environment 2 Large molecule to study Rationale and Challenges 2. K. E. Amunson and J. Kubelka. J. Phys. Chem. B. 111, 9993 (2007)

Producing Variable Amounts of Orthohydrogen and Parahydrogen 3,4 nH 2 pH 2 3. S. Tam and M. E. Fajardo. Rev. Sci. Instrum. 70, 1926 (1999 ) 4. Yoshioka, K., Raston, P. L., and D. T. Anderson. Int. Rev. Phys. Chem. 25, 469 (2006) Cryostat cold tip Fe(OH) 3 catalyst T=14-80K Obtain variable amounts of parahydrogen (pH 2 ) and orthohydrogen (oH 2 )

FTIR Beam nH 2 Bruker IFS 120 HR FTIR FTIR Beam MCT Detector BaF 2 substrate o/p converter Chemical dopant Synthesis of NMA-doped pH 2 Crystals 5 5. M. E. Fajardo and S. Tam. J. Chem. Phys. 108, 4237 (1998)

Experimental Setup pH 2 NMA FTIR

NMA Compared with Formic Acid 6 6. L. O. Paulson and D. T. Anderson. J. Phys. Chem. A. 113, 1770 (2009) NMA 0.005% oH 2 NMA 51% oH 2 Formic Acid 0.005% oH 2 Formic Acid 51% oH 2

Matrix Shift as a Function of oH 2 Concentration 7. J. Kubelka and T. A. Kiederling. J. Phys. Chem. A. 105, (2001) Gas phase NMA Amide I gas phase frequency 7 is 1731 cm % oH 2 51% oH 2 Δν matrix =ν para -ν gas (cm -1 ) 51% ortho0.005% ortho (1.59%)-23.5 (1.36%)

Intermolecular Interactions in the Matrix J=0 pH 2 J=1 oH 2

Matrix Shift Effect pH 2 oH 2 NMA ν=1 ν=0 Gas phase In pH 2 In pH 2 with trace oH 2 In pH 2 /oH 2 mixture 1731 cm cm cm cm -1

Frequency Shift due to Orthohydrogen Amount 0.005% oH 2 51% oH cm cm -1

The Environment of the Matrix NMA Temp. increases Increased diffusion 8 allows for oH 2 molecules to move about in the matrix at 4.3K There is a greater electrostatic interaction between the oH 2 quadrupole and NMA dipole moments, causing the oH 2 molecules to agglomerate around the NMA dopant 9 8. J. van Kranendonk. Solid Hydrogen (Plenum, New York, 1983) 9. K. Yoshioka and D. T. Anderson. J. Chem. Phys. 119, 4731 (2003) 1.8K4.3K

Temperature Effects 51% oH % oH K 4.36K 1.92K 1.83K 4.34K 1.65K

NMA Widths with Variable oH 2 Concentrations 0.005% oH 2 FWHM=4.5 cm -1 51% oH 2 FWHM=1.8 cm -1

NMA Matrix Environment at High Orthohydrogen Concentrations oH 2 pH 2 NMA NMA is surrounded by oH 2 molecules Results in a primarily homogeneous environment

Linewidths due to the Matrix Environment 0.005% oH 2 FWHM=4.5 cm -1 51% oH 2 FWHM=1.8 cm -1 Inhomogeneous Homogeneous Broad Asymmetric Narrow Symmetric

Summary NMA Amide I mode is extremely sensitive to its environment NMA Amide I mode remains broad in solid pH 2 due to residual oH cm cm cm cm -1 Δν p-o =ν ortho -ν para (cm -1 ) Formic AcidNMA NMA Formic Acid Red=0.005% oH 2 Blue=51% oH 2

Acknowledgments Dr. David T. Anderson Ms. Sharon C. Kettwich Ms. Elsbeth Klotz NSF for the funding Thank you for listening!! See S.C.K.’s talk on Wednesday