THE ELECTRONIC SPECTRUM OF PYRIDINE IN GAS PHASE AND IN RARE GAS MATRICES

Author Institution:The absorption spectrum of pyridine in gas phase and rare gas matrices was studied in the spectral region extending from 1700 {\AA} to 2900 {\AA}. The main results show: (a) The 2900 {\AA} $(n \to \pi^{*})$ transition is similar to the corresponding gas phase transition. Only one $n\to \pi^{*}$ transition is observed. (b) In the absorption spectrum of the 2600 {\AA} $\pi\to\pi^{*}$ transition $(^{1}A_{1g}\rightarrow ^{1}B_{2u}$ in benzene symmetry) progressions are found with intervals of $900 cm^{-1} (\nu_{2})$ starting at the origin and at distance of $330cm^{-1} [\nu_{20}(b_{1})], 460cm^{-1} [\nu_{18}(b_{1})], 550cm^{-1} [\nu_{18}(a_{1})]$ and $725cm^{-1} [\nu_{11}(a_{1})]$ from the origin. (c) Two progressions were observed for the second $\pi \to \pi^{*}$ transition $(^{1}A_{1g} \to; ^{1}B_{2u}$ in benzene symmetry) the intervals being $900cm^{-1} (\nu_{20})$ starting at the origin and at 500cm${-1} (\nu_{18})$ from the origin. (d) One progression of 900cm${-1} (\nu_{2})$ was observed for the third $\pi\to \pi^{*}$ transition $(^{1}A_{1g} \to ^{1}E_{1u}$ in benzene symmetry). The spectrum represents no evidence for the splitting of the $^{1}E_{1u}$ state. (e) The transition to the $^{1}E_{2g}$ state (in benzene symmetry) was not observed