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Spectroscopy on triphenylamine and its van der Waals complexes

Authors
Journal
Chemical Physics
0301-0104
Publisher
Elsevier
Publication Date
Volume
163
Issue
2
Identifiers
DOI: 10.1016/0301-0104(92)87104-h
Disciplines
  • Physics

Abstract

Abstract Both vibrationally and rotationally resolved spectra of the S 1←S 0 transition in jet-cooled triphenylamine (TPA) around 340-320 nm are reported. Medium resolution spectra (0.5–1.0 cm −1 resolution) are recorded using (1 + 1)-resonance enhanced multi photon ionization (REMPI) with mass selective time-of-flight (TOF) detection in a pulsed molecular beam apparatus. The origin of the S 1←S 0 transition is at 29520.7 cm −1, higher than halfway to the ionization potential (IP) found at 6.89 eV. A vibratioal progression in the symmetric torsion mode (114 cm −1) as well as in the symmetric CN stretching mode (280 cm −1) is observed in the electronic spectra. The spectrum of the most abundant isomer of the TPA-Ar (TPA-Kr) complexes is blue-shifted by 211 cm −1 (216 cm −1) with respect to the spectrum of the free TPA molecule. High-resolution (the resolution mainly being determined by the natural linewidth of the transition, i.e. 36 MHz) spectra are recorded using laser induced fluorescence (LIF) in a cw molecular beam apparatus. Individual rotational transitions are resolved and the spectrum shows unambiguously that TPA is a symmetric top molecule. The rotational constant B″ in the S 0 state of TPA is equal to B″ = 403.7 ± 0.5 MHz. Upon S 1←S 0 excitation both B and C increase with 7.4 ± 0.1 MHz and 2.8 ± 0.1 MHz, respectively. The spectrum of the blue-shifted TPA-Ar isomer is the spectrum of a symmetric top molecule as well, and therefore the Ar atom has to be located on the C 3 symmetry axis, either on top of or underneath the umbrella formed by the phenyl rings. It appears that when Ar or Kr forms a complex with TPA, the first Ar, Kr, atom goes preferentially in a position on the C 3 symmetry axis of TPA, a position which causes an abnormal blue-shift of the spectrum. With the first rare-gas atom located in this special position, the second rare-gas atom is forced into a “normal” position, i.e. above one of the phenyl rings, causing a normal red-shift with respect to the TPA-Ar complex.

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