University of Pennsylvania ScholarlyCommons Publicly Accessible Penn Dissertations 2012 IR-UV Spectroscopic Studies of OH and CN Radical Complexes Bridget Anne O'Donnell University of Pennsylvania, [email protected] Follow this and additional works at: https://repository.upenn.edu/edissertations Part of the Chemistry Commons Recommended Citation O'Donnell, Bridget Anne, "IR-UV Spectroscopic Studies of OH and CN Radical Complexes" (2012). Publicly Accessible Penn Dissertations. 558. https://repository.upenn.edu/edissertations/558 This paper is posted at ScholarlyCommons. https://repository.upenn.edu/edissertations/558 For more information, please contact [email protected]. IR-UV Spectroscopic Studies of OH and CN Radical Complexes Abstract Infrared action spectroscopy is used to identify the OH-HONO2 complex, an intermediate proposed to be important in the reaction of OH with HONO2. Two features are observed in the OH stretching region: a rotationally structured band corresponding to the OH radical stretch and a broadened feature assigned to the OH stretch of HONO2. Assignments are based on vibrational frequencies, analysis of rotational structure, and comparison with ab initio calculations. Nascent OH product state distributions give a binding energy of ≤5.3 kcal mol-1. Infrared action spectroscopy is also used to examine the H2O-HO complex, a primary interaction in the hydration of OH. A rotationally structured band is assigned to the OH radical stretch of H2O-HO. The stability of the complex, ≤5.14 kcal mol-1, is derived from the nascent OH product state distribution. The assignment is supported by ab initio predictions of the spectral shift and dissociation energy. A second feature to lower frequency is attributed to a hot band from an H2O bending state based on theoretical modeling. IR-UV double resonance spectroscopy is used to characterize hindered rotor states in the ground electronic state of CN-Ne and CN-Ar. Infrared spectra exhibit perturbations due to Coriolis coupling: a deperturbation analysis gives rotational constants and coupling strengths. The energetic ordering and spacings of the hindered rotor states provide a probe of the anisotropic intermolecular potential, which is compared with ab initio calculations. The CN monomer is nearly free rotor-like within both complexes. A similar approach yields the infrared spectrum of H2-CN, which exhibits rotational structure consistent with ortho-H2-CN in a linear C≡N-H-H configuration. Lastly, laser-induced fluorescence and IR-UV fluorescence depletion studies are used to characterize the lowest intermolecular levels of CN-Ar correlating with CN B 2Σ+ + Ar. Fluorescence depletion spectra confirm that specificeatur f es originate from a common ground state. The observed energy level pattern and intensity profile eflectr the change in configuration from a weakly anisotropic potential about linear N≡C-Ar in the ground state to linear C≡N-Ar in the excited electronic state. Degree Type Dissertation Degree Name Doctor of Philosophy (PhD) Graduate Group Chemistry First Advisor Marsha I. Lester Keywords cyano radical, hydrogen bond, hydroxyl radical, infrared spectroscopy, rare gas Subject Categories Chemistry This dissertation is available at ScholarlyCommons: https://repository.upenn.edu/edissertations/558 IR-UV SPECTROSCOPIC STUDIES OF OH AND CN RADICAL COMPLEXES Bridget A. O’Donnell A DISSERTATION in Chemistry Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy 2012 Supervisor of Dissertation __________________________ Marsha I. Lester Edmund J. Kahn Distinguished Professor Graduate Group Chairperson __________________________ Gary A. Molander, Hirschmann-Makineni Professor of Chemistry Dissertation Committee Michael R. Topp, Professor of Chemistry Jeffery G. Saven, Associate Professor of Chemistry Feng Gai, Professor of Chemistry Dedication To my parents, for their unending support. ii Acknowledgements I owe many thanks to those who have supported and encouraged me throughout my graduate career at Penn. First of all, my advisor Marsha Lester, who has been a wonderful mentor and advisor. I would also like to thank my dissertation committee, Prof. Michael Topp, Prof. Feng Gai, and Prof. Jeffrey Saven, for helpful discussions and guidance. I would also like to thank members of the Lester research group, past and present, who have helped me along the way. Thanks especially to Joseph Beames, who I have worked closely with over the past two years and is more talented than he would care to admit. Thanks also to current graduate students Julia Lehman and Fang Liu. I wish both of you the best of luck at Penn. I would also like to thank past members Eunice Li, Ian Konen, Craig Murray, Logan Dempsey, and Erika Derro, for being patient with me as I began my research and adjusted to the steep learning curve. Last, but certainly not least, I would like to thank my family. To my parents, who have been incredibly supportive of me throughout my academic career and, without whom, I could not have made it to where I am. To my siblings Janey, Ryan, Erin, and Casey, thank you for keeping me sane throughout this process. And finally, to my husband Rob, who has been incredibly patient, I can’t thank you enough for sticking by me through everything. iii Abstract IR-UV SPECTROSCOPIC STUDIES OF OH AND CN RADICAL COMPLEXES Bridget A. O’Donnell Marsha I. Lester Infrared action spectroscopy is used to identify the OH-HONO2 complex, an intermediate proposed to be important in the reaction of OH with HONO2. Two features are observed in the OH stretching region: a rotationally structured band corresponding to the OH radical stretch and a broadened feature assigned to the OH stretch of HONO2. Assignments are based on vibrational frequencies, analysis of rotational structure, and comparison with ab initio calculations. Nascent OH product state distributions give a binding energy of ≤5.3 kcal mol-1. Infrared action spectroscopy is also used to examine the H2O-HO complex, a primary interaction in the hydration of OH. A rotationally structured band is assigned to -1 the OH radical stretch of H2O-HO. The stability of the complex, ≤5.14 kcal mol , is derived from the nascent OH product state distribution. The assignment is supported by ab initio predictions of the spectral shift and dissociation energy. A second feature to lower frequency is attributed to a hot band from an H2O bending state based on theoretical modeling. IR-UV double resonance spectroscopy is used to characterize hindered rotor states in the ground electronic state of CN-Ne and CN-Ar. Infrared spectra exhibit iv perturbations due to Coriolis coupling: a deperturbation analysis gives rotational constants and coupling strengths. The energetic ordering and spacings of the hindered rotor states provide a probe of the anisotropic intermolecular potential, which is compared with ab initio calculations. The CN monomer is nearly free rotor-like within both complexes. A similar approach yields the infrared spectrum of H2-CN, which exhibits rotational structure consistent with ortho-H2-CN in a linear C≡N–H-H configuration. Lastly, laser-induced fluorescence and IR-UV fluorescence depletion studies are used to characterize the lowest intermolecular levels of CN-Ar correlating with CN B 2Σ+ + Ar. Fluorescence depletion spectra confirm that specific features originate from a common ground state. The observed energy level pattern and intensity profile reflect the change in configuration from a weakly anisotropic potential about linear N≡C–Ar in the ground state to linear C≡N–Ar in the excited electronic state. v Table of Contents Abstract............................................................................................................................. iv Table of Contents ............................................................................................................. vi List of Tables .................................................................................................................... xi List of Figures.................................................................................................................xiv Chapter 1 Introduction................................................................................................1 References..................................................................................................19 Chapter 2 Spectroscopic Identification and Stability of the Intermediate in the OH + HONO2 Reaction ...........................................................................24 I. Introduction................................................................................................25 II. Results........................................................................................................29 A. Infrared Action Spectra........................................................................29 B. OH Product State Distribution.............................................................36 C. Insights From Theory...........................................................................40 III. Discussion..................................................................................................44 IV. Materials and Methods...............................................................................46 References..................................................................................................49 Chapter 3 Infrared Spectrum and Stability