Kristjan Haller

HIGH-TEMPERATURE VAPOR-PHASE RAMAN SPECTRA AND ASSIGNMENT OF THE LOW-FREQUENCY MODES OF TRANS-STILBENE AND 4-METHOXY-TRANS-STILBENE

Abstract The vapor-phase Raman spectra of trans -stilbene at 330°C and 4-methoxy- trans -stilbene at 350°C have been recorded using a specially constructed high temperature cell. Together with the dispersed fluorescence spectra, these spectra have been used to assign the eight low-frequency vibrational modes in each molecule. For trans -stilbene, strong polarized bands at 273 and 152 cm −1 were ascribed to the totally symmetric ν 24 (C e -phenyl bend) and ν 25 (in-plane phenyl wag), respectively. A depolarized band at 207 cm −1 was assigned to the B g phenyl flap ( ν 47 ), and a polarized shoulder near 125 cm −1 is believed to result from both the B g phenyl torsion ( ν 48 ) and the overtone of the A u phenyl flap ( ν 36 ). For 4-methoxy- trans -stilbene the C e -phenyl bend and in-plane phenyl wag were shifted to 234 and 144 cm −1 , respectively. These assignments were critical for understanding the fluorescence spectra associated with the torsional motions.

Raman spectroscopy of vapors at elevated temperatures

The most effective way to obtain high quality vapor-phase Raman spectra is to heat the samples to increase their vapor pressure. Many samples can be heated to 350 °C and higher without decomposition. We have designed a simple Raman cell to allow these high temperature studies to be carried out. The high-temperature Raman spectra of nine molecules will be presented and discussed. Most of these are non-rigid molecules containing aromatic rings for which vibrational potential energy surfaces have been determined from their spectra. Two molecules (p-cresol and 3-methylindole) are model compounds for amino acids and their vapor-phase spectra are characteristic of environments with no hydrogen bonding.

A computer-controlled apparatus for laser-induced fluorescence spectroscopy in a supersonic jet

Abstract An experimental apparatus for laser-induced fluorescence excitation spectroscopy (FES) and for dispersed fluorescence studies in a supersonic jet has been constructed and optimized for the collection of spectra from weakly fluorescing samples. A detailed description of the hardware and software is presented here.