Title

Threshold Photoelectron Photoion Coincidence Spectroscopy of Toluene and Cycloheptatriene

Poster Number

2a

Lead Author Affiliation

PCSP

Lead Author Status

Doctoral Student

Second Author Affiliation

Chemistry

Second Author Status

Faculty

Third Author Affiliation

-

Third Author Status

Staff

Fourth Author Affiliation

-

Fourth Author Status

Staff

Fifth Author Affiliation

Chemistry

Fifth Author Status

Faculty

Introduction

Both toluene (TOL) and cycloheptatriene (CHT) molecular ions can lose a hydrogen radical to form C7H7+, which can have several possible structures, such as benzyl, tolyl, and tropylium ion. It is generally accepted that a rapid interconversion can happen between the toluene and cycloheptatriene molecular ions at threshold energy. It is also well-known that the tropylium ion is the most stable isomer of the C7H7+ ion, whereas the benzyl ion has slightly higher energy. The tropylium ion has been a matter of some debate over the last 50 years.

Purpose

There are still larger than expected differences between experimental and high-level calculation 0 K appearance energy and heat of formation data.

Method

The dissociative photoionization of toluene and 1,3,5-cycloheptatriene was studied by Imaging Photoelectron Photoion Coincidence (iPEPICO) Spectroscopy. The molecular ions were prepared by vacuum ultraviolet photoionization and their lowest energy dissociation channel was studied, where the energy selected molecular ions lose a hydrogen atom.

Results

We have used PEPICO spectroscopy to record the breakdown diagrams of both CHT and TOL. RRKM statistical analysis was employed to model the experimental breakdown diagrams and to determine the 0 K appearance energy of the fragment ions. The reaction mechanism of the hydrogen loss channel was explored by quantum chemical calculations to map out the potential energy surface leading to tropylium and benzyl ions.

Significance

The almost 50-year long debate is resolved on the energetics, formation and the relative abundances of tropylium and benzyl ions near threshold.

Location

DeRosa University Center

Format

Poster Presentation

Poster Session

Afternoon 1pm-3pm

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Apr 28th, 1:00 PM Apr 28th, 3:00 PM

Threshold Photoelectron Photoion Coincidence Spectroscopy of Toluene and Cycloheptatriene

DeRosa University Center

Both toluene (TOL) and cycloheptatriene (CHT) molecular ions can lose a hydrogen radical to form C7H7+, which can have several possible structures, such as benzyl, tolyl, and tropylium ion. It is generally accepted that a rapid interconversion can happen between the toluene and cycloheptatriene molecular ions at threshold energy. It is also well-known that the tropylium ion is the most stable isomer of the C7H7+ ion, whereas the benzyl ion has slightly higher energy. The tropylium ion has been a matter of some debate over the last 50 years.