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

Abstract

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 behavior of tropolone is analyzed in the accompanying article.

Coherent Proton Tunneling in Hydrogen Bonds of Isolated Molecules: Malonaldehyde and Tropolone

“…1.5 [3121, 3102 cm -1 in Ne-isolated TRN(OH)] occurs near the five CH stretching fundamentals (overlapped at 3063, 3030 cm -1 ), with anharmonic resonance couplings to these and many (perhaps all) of the binary overtone and combination states present in the region. The broad gas phase absorption for TRN(OH) closely spans the limits set by these transitions (as [34]. In Ne-isolated TRN(OH) the fundamental OH stretching spectral doublet is at 3121 cm -1 and a shoulder at 3102 cm -1 .…”

“…Of these, ten pairs of lines were originally assigned as apparent spectral doublets, but in later experimental and computational research [34,86] virtually all of the extraneous lines were assignable as binary, and some ternary, overtone and combination transitions. Relative absorption intensities suggest the anharmonic resonance interactions couple many of the vibrational states, and several weak computed fundamentals of TRN(OH) and TRN (OD) have not yet been observed in IR spectroscopic experiments.…”

“…1.5 shows peaks appear in the region. Vibrational assignments [34,86] were proposed on the basis of (i) gas phase IR spectra at lower frequencies, (ii) moderately high level MO computations, (iii) two-laser fluorescence dip IR spectra (FDIRS) of jet-cooled TRN(OH) and TRN(OD) by Frost et al [33], (iv) the IR spectra of Ne matrix-isolated samples [24], and (v) the results of independent theoretical computations of the spectral doublet for the OH stretching fundamental. The weak OH stretching fundamental assigned in Fig.…”

“…Giese and Kühn [92] applied a multidimensional reaction surface approach to TRN using 4D and 12D versions of the reaction surface. The 4D surface included reduced normal modes favoring OH stretch, COH bend, the skeletal mode near 750 cm -1 presented [34,86] as the tautomerization coordinate, and O_O stretching. The 12D model was used to compute IR spectra using the multiconfiguration time-dependent Hartree method.…”

“…MA has 21 and TRN has 39 internal coordinates available for coupling into their tunneling processes. MA, with a developing experimental base [9][10][11][12][13][14][15][16][17][18][19][20][21], holds a computational edge over TRN which currently stands alone in its size group for its catalog of spectroscopic tunneling structures [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. With 15 atoms TRN is reasonably expected to model elements of the intramolecular dynamical behavior occurring in much larger molecules, and it is amenable to high level experimental and theoretical studies.…”