Selective IR Laser Induced Isomerization and Dissociation of BIS (Trifluoromethyl) Ketene Molecules

V B Laptev,L M Tumanova,E A Ryabov

doi:10.1155/1996/34032

Abstract

Multiphoton IR laser induced isomerization and dissociation of (CF3)2C=C=O (FMK) molecules have been studied. The antisymmetric stretch v1 = 2192 cm-1 of C=C=O—and antisymmetric v16 = 991 cm-1 of C—C— bonds were excited by the second- and first harmonics of a pulsed TEA CO2 laser. The dependence of isomerization conversion on laser radiation frequency, fluence, and number of shots was measured. The isomerization channel was predominant compared with dissociation for the conditions of IR multiphoton excitation under study.The isomerization of FMK by the second–harmonic radiation of a CO2 laser was proved to be selective with respect to oxygen isotopes. The isomerization product (FMA molecules) was enriched with 18O with maximum value of selectivity α(18/16) = 3.9 when FMK molecules were excited at 2ωlas = 2143.8 cm-1.

Highlights

The effect of vibrational multiphoton excitation and dissociation (MPD) of polyatomic molecules by powerful IR laser radiation has been under intense studies in many laboratories of the world since the early seventies and remains under investigation as regards photochemical processes and its potential applications-laser chemical synthesis, isotope separation, etc. 1’2 Less attention has been given to isomeric transformations resulting from MP excitation
Were detected by a mass spectrometer. The latter is an indication of some dissociation of FMK molecules
The amount of FMA increases only at the starting of irradiation and begins to drop. Such behaviour can be attributed to the dissociation of the accumulating isomer

Summary

Introduction

The effect of vibrational multiphoton excitation and dissociation (MPD) of polyatomic molecules by powerful IR laser radiation has been under intense studies in many laboratories of the world since the early seventies and remains under investigation as regards photochemical processes and its potential applications-laser chemical synthesis, isotope separation, etc. 1’2 Less attention has been given to isomeric transformations resulting from MP excitation. To understand what products are formed as a result of dissociation of FMK itself we recorded them after irradiation of the sample by a single laser pulse. 1 The quantitative and qualitative composition of the products, resulting from MP excitation of FMK, depends on the excitation level which is determined, in turn, by laser radiation fluence.

Results

Conclusion