Richard L. Redington

Vibrational spectra and normal coordinate analysis of isotopically labeled formic acid monomers

Present address of Duane R, Kirklin: National Bureau of Standards, Washington, D. C., 20234. Ellis R, Lippincott: Posthumous.

Laser fluorescence excitation spectrum of jet‐cooled tropolone: The à 1B2–X̃ 1A1 system

Five of the lowest frequency species a1, b1, and b2 vibrational modes of tropolone in the A 1B2 electronic state are studied using high resolution laser fluorescence excitation spectroscopy of the jet‐cooled sample. The ν’26(b1) mode at 38 cm−1, most probably a ‘‘folding’’ vibration of the seven‐membered and O⋅⋅⋅HO chelated ring systems of tropolone, is observed in the progression 26v0 with primarily even valued quantum numbers to v26=14. Tunneling doublets in the progression are observed to decrease from 18.90 cm−1 in the vibrationless state to unresolvable values when v’26 is larger than 8, thereby demonstrating highly mode‐specific quenching of the ‘‘H atom’’ tunneling process by these low frequency, out‐of‐plane, ring deformation vibrations. The progression 251026v0 is observed to v26=9 and no tunneling doubling is resolved for any of the transitions. These progressions show that the tunneling energy level splitting of tropolone in the vibrationless level of the ground electronic state can be at most...

Tropolone monomer: Vibrational spectrum and proton tunneling

Abstract Infrared matrix-isolation spectra are reported for the tropolone monomers C 7 H 5 O 2 H and C 7 H 5 O 2 D. Tropolone possesses an intramolecular hydrogen bond and the possibility for proton tunneling from one oxygen atom to the other. Clearcut multiplets attributed to tunneling are observed for the OD stretching mode and for heavy atom modes of both C 7 H 5 O 2 D and C 7 H 5 O 2 H. The (mixed) carbonyl stretching mode particularly seems to facilitate tunneling from one conformation to the other. The tunneling phenomena suggests that tropolone monomer has nearly C 2 v symmetry. As a crude estimate, the tunneling potential energy barrier is calculated to be less than 5600 cm −1 in the ground electronic state of C 7 H 5 O 2 D. The barrier is lower in the Π ∗ electronic state than in the ground electronic state. A vibrational assignment that encompasses most of the 39 fundamental modes is proposed. The vibrations are classified using C 2 v symmetry species and a parallel vibrational analysis is presented for tropone, C 7 H 6 O, which is a true C 2 v molecule.

Infrared Spectra of Matrix‐Isolated Acetic Acid Monomers

Infrared spectra of monomeric acetic acids [CH3COOH(D) and CD3COOH(D)] isolated in Ar and N2 matrices near 4°K are reported. A large anharmonic potential‐energy contribution is evident from the observed isotopic frequency shifts. It is proposed that this arises primarily from the double‐minimum potential‐energy curve for tunneling of the H atom between O atoms via the COH angle bending coordinate. In all cases, important coupling between the COH angle bending and C–O stretching coordinates is observed, with a strong addition of CD3 (umbrella) angle deformation in the case of CD3COOH. Exceptional matrix effects are observed for the coupled vibrations of the –OH molecules. A complete assignment is proposed for these acetic acids on the basis of the new data. As additional supporting evidence, the spectrum of matrix‐isolated CH3COF and of acetic acid vapor at low pressure and long path length are reported.

On the OH Stretching and the Low‐Frequency Vibrations of Carboxylic Acid Cyclic Dimers

Infrared spectra for the hydroxyl stretching region of matrix‐isolated CF3COOH, CF3COOD, and CH3COOH are reported, and the vapor‐phase spectrum of CF3COOH in the region below 500 cm−1 is given. Characteristic line spacings that are found to reproduce the observed spectral features of the high‐frequency region are also found to be associated with the low‐frequency spectra. Fundamental frequencies for the cyclic dimer ring vibrations are suggested. It is concluded that the well‐known band broadening in the hydroxyl stretching region is due to combination bands of the low‐frequency modes with the OH fundamental vibration and with nearby binary excitations of the COH(D) bending and the C–O stretching vibrations. A model such as that proposed by Marechal and Witkowski, which considers interactions between the low‐frequency and the high‐frequency vibrations, seems appropriate in order to explain the intensities of the high combination bands that occur. Further emphasis for the unusual vibrational properties of ...

Infrared spectra of trifluoroacetic acid and trifluoroacetic anhydride

Spectra of matrix-isolated trifluoroacetic acid species and matrix-isolated and solid trifluoroacetic anhydride are reported. Vibrational assignments are given for the CF3COOH and CF3COOD monomers, the i.r. active vibrations of (CF3COOH)2 and (CF3COOD)2 cyclic dimers, and (CF3CO)2O. The analysis suggests that a very low barrier hinders internal rotation of the CF3 group in the acids and also indicates the probable absence of an equilibrium plane of symmetry in the monomers. The truth of these statements hinges on the interpretation of the data for the nominal COH bending vibration. For CF3COOH monomer this band shows two components that are separated by ~15 cm−1, while CF3COOD monomer yields a single, sharp band that is red-shifted by a normal amount. These observations, coupled with the anomalous isotopic frequency behavior found for this vibration with acetic acid monomers [C.V. Berney, R.L. Redington and K.C. Lin, J. Chem. Phys.53, 1743 (1970)], reinforces the suggestion that a relatively low barrier hinders H atom transfer between the two O atoms via a coordinate that originates as COH angle bending.

Infrared Spectra of Matrix‐Isolated ClF3, BrF3, and BrF5; Fluorine Exchange Mechanism of Liquid ClF3, BrF3, and SF4

The infrared spectra of matrix‐isolated ClF3, BrF3, and BrF5 have been investigated in the region from 800 to 33 cm−1. All six fundamentals have been observed in Ar and N2 matrices for ClF3 and BrF3, which are planar T‐shaped molecules, and most of them in a Ne matrix. The two lowest‐frequency fundamentals, which could not be separated in the gas‐phase spectra [H. Selig, H. H. Claassen, and J. H. Holloway, J. Chem. Phys. 52, 3517 (1970)] are clearly visible in the matrix‐isolation spectra. Both molecules show only small gas‐matrix frequency shifts, and multiplet structure for both molecules suspended in Ar matrices may be understood in terms of isotope and matrix site effects. Several absorption bands found at low matrix‐isolation ratios are attributed to dimers and a tentative partial vibrational assignment is presented. Similar dimer structures are assumed for both substances. The structure seems best represented with two F bridges formed using the long‐bond F atoms. The structure is favored by the x‐ra...

Heavy atoms and tunneling in the X̃ state of tropolone

Large (6.9 to 16.3 cm−1 ) tunneling splittings are uniquely observed for the ν27 (OD stretch), ν31 (carbonyl stretch), and ν34 (C=C–C stretch) fundamentals of tropolone‐OH and tropolone‐OD in the X 1A1 (ground) electronic state. These same three modes are predicted by the molecular geometry to interact strongly with tunneling because the dominant vibrational and tunneling displacements involve the same atoms. The heavy atom tunneling displacements (≊0.07 A) are small enough to plausibly consider heavy atom tunneling phenomena—especially in appropriate excited vibrational states—and the tunneling splittings appear consistent with behavior expected at zero order for adiabatic reaction surface theory with a 2D reaction surface defined by C=O/C–O and C=C–C heavy atom coordinates. This model attributes tunneling in the X state of tropolone to heavy atom motion followed adiabatically by H atom motion rather than the reverse. Energy balance equations are used to obtain estimates for the vibrational state‐speci...

H atom and heavy atom tunneling processes in tropolone

The minimum energy pathway leading between the tautomers of tropolone was calculated using molecular orbital (MO) methods. This, with various 1D and 2D cuts of the potential energy surface (PES) topography, reveals the {tunneling skeleton}/{tunneling H atom} mechanism for tautomerization. In the zero-point states the H atom is localized to one of the O atoms until the tropolone skeleton becomes sufficiently vibrationally displaced towards C2v configurations that near-equal double-minimum potential energy functions (PEFs) arise for the H atom vibration. The resulting delocalization of the H atom between the two O atom sites allows the skeletal displacement to proceed through the barrier and the tautomerization process to be completed. The v1 (OH stretching) energies in quantum states N1 are strongly dependent on the skeletal geometry and, adiabatically separated from the slow v22 vibration, they contribute to markedly different 1D effective potential energy functions V22eff[N1] for v22. V22eff[N1=0] is a n...

IR spectra of tropolone(OH) and tropolone(OD)

Infrared spectra of tropolone(OH) and tropolone(OD) obtained from vapor phase, solvated, and rare gas matrix-isolated samples, and from fluorescence dip infrared spectroscopy experiments by Frost et al. on jet-cooled samples, are analyzed with the guidance of high level ab initio molecular orbital (MO) computations. It is found that the anharmonicity of the double minimum global potential energy surface of S0 tropolone is manifested by multistate local resonance networks coupling fundamental vibrations to nearby overtone and combination states. These resonance networks pervade the IR spectrum of tropolone above 500 cm−1, and the absorbances are much more strongly perturbed from harmonic level predictions than the frequencies. Some of the IR absorbances are also sensitive to intermolecular interactions. At maximum spectral resolutions reaching ∼0.2 cm−1 only the v1 and v22 (OH stretching and nascent skeletal tunneling) vibrations show resolved vibrational state-specific tunneling doublets. The tunneling be...