Abstract

← Table of Contents


Ring-opening dynamics of 1,3-cyclohexadiene studied by time-resolved molecular orbital spectroscopy

HT-01

Ring-opening dynamics of 1,3-cyclohexadiene studied by time-resolved molecular orbital spectroscopy


T. Sekikawa1*, R. Iikubo1, Y. Harabuchi2, T. Taketsugu2

1Department of applied physics, Hokkaido university, Sapporo, Japan

2Department of chemistry, Hokkaido university, Sapporo, Japan

Chemical bonds in a molecule are characterized by the electron spatial distributions, which are well understood by a molecular orbital (MO) theory. The ionization energy of each MO, measured by photoelectron spectroscopy, is correlated with its orbital energy under Koopmans’ theorem. Therefore, by observing time-resolved photoelectron spectroscopy (TRPES) with high harmonic pulses [1], we can gain insight into transient molecular geometries and determine the location where chemical reactions take place, which is called time-resolved MO spectroscopy [2]. In this work, we investigated the ring-opening dynamics of 1,3-cyclohexadiene. Figure 1 shows the photoelectron spectrum and the corresponding MOs of 1,3-cyclohexadiene. Figure 2 shows the photoelectron spectrogram probed by 29.5-eV high harmonic pulses [1]. The photoelectron intensity from σC-C observed around 13 eV was decreased within the excitation pulse duration and was constant upto 600 fs, while those from σC=C and πC=C around 11.5 eV were increased gradually. After 600 fs, the photoelectron intensities of these MOs, σC-C, σC=C and πC=C, were increased. The C-C single bond breaks by the ring-opening reaction upon photoexcitation, while the C=C double bonds remain. Therefore, these MO-dependent dynamics suggests that the ring-opening reaction proceeds during 600 fs. Time-resolved MO spectroscopy can probe the conformal changes sensitively.

Figure 1 Figure 2: Photoelectron spectrogram

Figure 1 Figure 2: Photoelectron spectrogram

References:

[1] M. Ito, Y. Kataoka, T. Okamoto, M. Yamashita, and T. Sekikawa, Opt. Express 18, 6701 (2010).

[2] A. Makida, H. Igarashi, T. Fujiwara, T. Sekikawa, Y. Harabuchi, and T. Taketsugu, J. Chem. Phys. Lett. 5, 1760 (2014).