Ultraviolet absorption cross sections for N2H4 vapor between 191–291 nm and H(2S) quantum yield in 248 nm photodissociation at 296 K

Abstract

The absolute UV absorption cross section of hydrazine vapor at 253.65 nm was determined to be, σ253.65=(2.859±0.172)×10−20 cm2 molec−1 (where the error is 1 sigma, precision plus systematic) at 296±2 K. The UV absorbance in a column of slowly flowing N2H4/He gas mixture was monitored in an absorption cell, and the eluting hydrazine collected and quantified by titration with standard KIO3 solution in HCl acid. The relative UV absorbance spectrum of N2H4 vapor was recorded from 191–291 nm using a diode-array spectrometer and normalized to absolute absorption cross sections using the σ253.65 value. The primary quantum yield of H(2S) formation in 248.3 nm photodissociation of N2H4 was measured to be 0.85±0.15 (where the error is 1 sigma, precision plus systematic) at 296±2 K relative to photolysis of CH3SH under similar experimental conditions. The observed spectrum is essentially continuous and the high H(2S) yield is consistent with unit dissociation to the lowest à 1A singlet excited state. Kinetics studies also yield a value for the rate coefficient, k1(296 K)=(1.48±0.22)×10−13 cm3 molec−1 s−1 for the reaction H+N2H4→products; (k1), where the error is 1 sigma, precision plus systematic.