Rotamers of o- and m-Dimethoxybenzenes Studied by Mass-Analyzed Threshold Ionization Spectroscopy and Theoretical Calculations

Abstract

We applied two-color resonant two-photon mass-analyzed threshold ionization (MATI) spectroscopy to investigate the molecular properties of the selected rotamers of o-dimethoxybenzene (ODMB) and m-dimethoxybenzene (MDMB). The present experimental results show that only one stable configuration is involved in the photoexcitation and ionization processes of ODMB, as predicted by theoretical calculations. The adiabatic ionization energy (IE) of ODMB is measured to be 61 617 ± 5 cm(-1). In the case of MDMB, both our experimental and calculated results suggest that there are three stable rotamers coexisting in the sample. The adiabatic IEs of rotamers a, b, and c are determined to be 63 523 ± 5, 64 491 ± 5, and 63 758 ± 5 cm(-1). Analysis on the MATI spectra shows that most of the active cation vibrations of these isomeric species result from in-plane ring motions. In addition, different orientations of the two OCH(3) groups have little effect on these vibrations.

Two-color resonant two-photon ionization and mass-analyzed threshold ionization spectroscopy of o-chloroanisole

“…The general features of these two spectra are nearly identical with the same E 1 of 35 745 ± 2 cm −1 . Similar to the cases of o-dimethoxybenzene [23] and o-fluoroanisole [24,25], only one stable isomer of o-chloroanisole is found to involve in the present R2PI and MATI experiments. The configuration interaction singles (CIS), time-dependent Becke three-parameter functional with the Lee-Yang-Parr functional (TD-B3LYP), and TD-B3PW91 methods with the aug-cc-pVDZ basis set predict the E 1 's of 43 723, 36 850, and 37 176 cm −1 , corresponding to overestimations of 22.3, 3.1, and 4.0%, respectively.…”

Rotamers of m-chloroanisole studied by two-color resonant two-photon mass-analyzed threshold ionization spectroscopy

“…achieved by comparing these data with those of anisole [24], mmethoxyaniline [25], m-fluoroanisole [27], and m-dimethoxybenzene [36], and the predicted values from the CIS/6-311G(d,p) calculations. The numbering system of the normal vibrations follows that used by Varsanyi [37] for benzene derivatives and is based on Wilson's notations [38].…”

Rotamers of <em>m</em>-Methylanisole Studied by Mass-Analyzed Threshold Ionization Spectroscopy

“…The MATI spectra of the selected rotamers were recorded by ionizing through a few intermediate vibronic states in the S1 state to obtain more information about the active cation vibrations. Comparison of the experimental data of m-methylanisole with those of anisole, 10 toluene, 11 and their derivatives [12][13][14][15][16][17][18][19][20][21] allows one to learn the substitution effects of the methyl and methoxyl groups on the transition energy and molecular vibration. We have also performed the ab initio and density function theory (DFT) calculations to provide possible interpretation of our experimental findings.…”