The infrared and Raman spectra of 2-cyclohexen-1-one and its 2,6,6-d3 isotopomer in their liquid and vapor phases have been recorded and a complete vibrational assignment was carried out. DFT theoretical calculations were carried out to predict the vibrational frequencies and the agreement is excellent.

A comprehensive spectroscopic study of 1,4-dihydronaphthalene (14DHN) has been carried out for its ground and S(1)(pi,pi*) electronic states using infrared, Raman, ultraviolet, and laser-induced fluorescence (LIF) spectroscopic techniques. The experimental work was complemented by ab initio and DFT calculations. For the ground state excellent agreement between observed and calculated values was attained. For the S(1)(pi,pi*) excited state 19 of the vibrational modes were clearly determined and excited vibronic levels for a number of these were also identified. A detailed energy map for the low-frequency modes in both electronic states was established. 14DHN is very floppy in its S(0) ground state but less so in its excited state. The floppiness relaxes C(2v) selection rules for the S(0) state.

Our previously published infrared and Raman spectra of 1,3-disilacyclobutane (13DSCB) and its 1,1,3,3-d4 isotopomer have been reexamined and partially reassigned on the basis of DFT and ab initio calculations. The calculations confirm previous microwave work that the CSiC angles in the ring are unexpectedly larger than the SiCSi angles. This may arise from the partial charges on the ring atoms. The calculations are in excellent agreement with the observed spectra in both frequency and intensity. They also demonstrate that this molecule has CH2 wagging and twisting vibrations with frequencies below 1000 cm-1, about 200 cm-1 lower than expected. These unprecedented low values can be explained by the decreased slope in the potential energy curves for these vibrations as the sideways motions of the CH2 groups result in attractive forces between the positively charged hydrogens on the carbon atoms and the negatively charged hydrogens on the silicon atoms. The theoretical calculations also confirm the previous conclusions that the individual molecules (vapor) have C2v symmetry whereas in the solid the molecules become planar with D2h symmetry. The vibrational coupling between the ring-angle bending mode and the SiH2 in-phase rocking, which is present for the C2v structure, is forbidden for D2h and hence disappears.

The cavity ringdown spectra of 2-cyclohexen-1-one (2CHO) and its 2,6,6-d3 isotopomer (2CHO-d3) have been recorded in the spectral region near their S1(n,pi)<--S0 band origins which are at 26,081.3 and 26,075.3 cm-1, respectively. The data allow several of the quantum states of nu39, the ring inversion, to be determined for both the ground and excited electronic states. These were utilized to calculate the one-dimensional potential energy functions which best fit the data. The barriers to inversion for the S0 and S1(n,pi) states were found to be 1,900 +/- 300 and 3,550 +/- 500 cm-1, respectively. Density functional theory calculations predict values of 2,090 and 2,265 cm-1, respectively.

The fluorescence excitation spectra, single vibrational level fluorescence spectra, and ultraviolet absorption spectra of 1,4-dihydronaphthalene have been analyzed. The first four quantum energy spacings for the ring-puckering vibration were determined for the S-0 and S-1(pi, pi*) electronic states, and the potential energy functions were also determined. In the ground state the single-minimum function is dominated by the quartic term, but in the excited state the function becomes nearly harmonic. The S-0 function is less rigid than that for 1,4-cyclohexadiene but the S-1(pi, pi*) function becomes much more rigid. Earlier work on this molecule had erroneously postulated barriers in both electronic states. (c) 2007 Elsevier B.V. All rights reserved.

Author Institution: Department of Chemistry, University of Wisconsin-\mbox{Eau Claire},; Eau Claire, WI 54702; Department of Chemistry, Hanyang University, Ansan 425-791,; Korea; Department of Chemistry, Texas A \& M University, College Station, TX 77843

Author Institution: Department of Chemistry, University of Wisconsin-\mbox{Eau Claire},; Eau Claire, WI 54702; Department of Chemistry, Hanyang University, Ansan 425-791,; Korea; Department of Chemistry, Texas A \& M University, College Station, TX 77843

The S1(n,π*) ← S0 cavity ringdown spectrum of 2-cyclohexen-1-one vapor has been recorded in the vicinity of the 000 band, which is at 26 089.1 cm–1. Observation of hot bands in the spectrum has permitted the determination of several low-frequency fundamentals and overtones in the ground electronic state. The lowest two excited quantum states for the inversion vibration (v39) were found to be at 99.0 and 197.0 cm–1. Together with previously published far-IR spectra and vapor-phase Raman spectra, the fundamental frequencies for v39, v38, and v37 have been determined. From observed v39 levels, the barrier to inversion has been determined experimentally to be 1900 ± 300 cm–1, which is very different from values of 935 and 3379 cm–1 previously reported from Raman and far-IR data, respectively. Density functional calculations carried out in this paper give a barrier value of 2090 cm-1 when the B3LYP/6-311+G(d,p) basis set is used.Key words: cavity ringdown spectra, 2-cyclohexen-1-one, Raman spectra, potential energy function, inversion barrier.

Abstract: The heating of samples sealed in special heatable glass cells [1] allows samples with high boiling points to be studied as vapors by Raman spectroscopy. The investigation of the potential energy surfaces (PESs) of non-rigid molecules in our laboratory [2,3] is typically complemented by the Raman spectra of the vapors as these nicely provide data not available from infrared and ultraviolet absorption and fluorescence measurements. Examples of molecules recently investigated are 2cyclohexenone, tetralin (TET), 1,4-benzodioxan (14BZD), and 3-methylindole, which are shown below in that order.

The S1(n,π*) ← S0 cavity ringdown spectrum of 2-cyclohexen-1-one vapor has been recorded in the vicinity of the 000 band, which is at 26 089.1 cm-1. Observation of hot bands in the spectrum has permitted the determination of several low-frequency fundamentals and overtones in the ground electronic state. The lowest two excited quantum states for the inversion vibration (ν39) were found to be at 99.0 and 197.0 cm-1. Together with previously published far-IR spectra and vapor-phase Raman spectra, the fundamental frequencies for ν39, ν38, and ν37 have been determined. From observed ν39 levels, the barrier to inversion has been determined experimentally to be 1900 ± 300 cm-1, which is very different from values of 935 and 3379 cm-1 previously reported from Raman and far-IR data, respectively. Density functional calculations carried out in this paper give a barrier value of 2090 cm-1 when the B3LYP/6-311+G(d,p) basis