Spectroscopic investigation of tetrahydroisoquinoline in supersonic jet

Abstract

Fluorescence excitation and dispersed emission spectra of tetrahydroisoquinoline are presented here. Two bands at 36 781 and 36 884 cm−1 are confirmed from the spectral hole burning studies as two origins for two conformers. These bands correspond to the inequivalent twist conformers with the hydrogen atom attached to the nitrogen atom at axial and equatorial positions, respectively. The former is found to be the most stable one. SVL spectra are explained on the basis of two theoretically calculated low-frequency vibrations. These correspond to the butterfly and puckering motions of the benzene chromophore, respectively.

Structure of hydrated clusters of tetrahydroisoquinoline [THIQ–(H2O)n=1,3] investigated by jet spectroscopy

“…2͑a͔͒, the electronic origin of the equatorial form is blueshifted by 103 cm Ϫ1 with respect to the axial form. 25 A difference in the blueshifts of the same order may be expected for the two corresponding monohydrates. As the origin of conformer e is 65 cm Ϫ1 blueshifted relative to the origin of conformer b, we assign conformer b to the axial and e to the equatorial form.…”

“…The vibrational modes of the two conformers have also been clearly identified by UV-UV hole-burning spectroscopy. 25 These features of the bare molecules have been discussed in one of our recent publications. 25 When water vapor is introduced in the sample chamber, in addition to the increase of intensity of some weak bands, a number of new bands appear in the LIF spectrum ͓Fig.…”

“…UV-UV hole-burning spectroscopy requires two UV light sources 25 and was carried out at Tohoku University. One UV source was generated by doubling the output of a dye laser ͑ND-6000͒ pumped by a Nd:YAG ͑Quanta Ray GCR 230͒ laser, and the other UV source was generated by doubling the output of a Lambda-Physik dye laser pumped by an excimer laser ͑Lamda Physik FL 2002͒.…”

“…24 Recently, we have identified by laser-induced fluorescence ͑LIF͒ and UV-UV hole-burning measurements two low-energy conformers of tetrahydroisoquinoline ͑THIQ͒ in a cold jet. 25 As shown in Fig. 1, the two conformers of THIQ are different with respect to the orientation of the N lone pair; that is, the two conformers have the H atom in either an equatorial or an axial orientation.…”

Chirality-dependent hydrogen bond direction in jet-cooled (S)-1,2,3,4-tetrahydro-3-isoquinoline methanol (THIQM): IR-ion dip vibrational spectroscopy of the neutral and the ion

“…The barrier can be estimated to be much higher than that deduced for the parent molecule THIQ (800 AE 350 cm À1 ), deduced from the spectroscopic data. 31 We can therefore safely deduce that Conformers I and II are trapped in their separate potential well in the conditions of the supersonic expansion.…”