A New Approach toward Transition State Spectroscopy

TL;DR

This paper introduces a novel application of Chirped-Pulse millimetre-Wave rotational spectroscopy to study photolysis transition states, providing insights into species populations and reaction pathways.

Contribution

It presents a new spectroscopic approach to analyze transition states in photolysis, focusing on vinyl cyanide and its photolysis products, with detailed spectral observations.

Findings

Detected vibrational levels of HCN and HNC post-photolysis

Did not observe vinylidene or certain acetylene vibrational levels

Discussed reasons for non-detection of vinylidene co-product

Abstract

Chirped-Pulse millimetre-Wave (CPmmW) rotational spectroscopy provides a new class of information about photolysis transition state(s). Measured intensities in rotational spectra determine species-isomer-vibrational populations, provided that rotational populations can be thermalized. The formation and detection of S0 vinylidene is discussed in the limits of low and high initial rotational excitation. CPmmW spectra of 193 nm photolysis of Vinyl Cyanide (Acrylonitrile) contain J=0-1 transitions in more than 20 vibrational levels of HCN, HNC, but no transitions in vinylidene or highly excited local-bender vibrational levels of acetylene. Reasons for the non-observation of the vinylidene co-product of HCN are discussed.