INFRARED-ABSORPTION OF CIS-ALKALI-METAL AND TRANS-ALKALI-METAL PEROXYNITRITES (MOONO, M=LI, NA, AND K) IN SOLID ARGON

Potassium nitrate (KNO3) isolated in solid argon at 13 K was irradiate d with emission from an ArF excimer laser at 193 nm. Recombination of the photofragments led to formation of both cis- and trans-potassium p eroxynitrites (KOONO). The cyclic conformer, cis-KOONO, absorbs at 144 4.5, 952.3, 831.6, and 749.1 cm(-1), whereas trans-KOONO absorbs at 15 28.4, 987.4, and 602.2 cm(-1) The assignments are based on observed O- 18- and N-15-isotopic shifts and comparison with similar compounds, ci s-cis and trans-perp HOONO. Ab initio calculations using density funct ional theory at a Becke3LYP level predicted similar line positions and isotopic shifts for both conformers. Photoconversion among these thre e isomers was achieved at various wavelengths and periods of irradiati on; cis-KOONO was photolyzed readily at 308 nm, whereas trans-KOONO in creased slightly in intensity initially and was eventually transformed to KNO3 on prolonged irradiation. Similar results were obtained for L iNO3 and NaNO3; cis-LiOONO and cis-NaOONO absorb at (1423.4, 1422.0), 966.2, 874.2, 792.3 cm(-1) and (1437.4, 1434.6), 961.4, 840.7, (770.9, 768.7) cm(-1) respectively, whereas trans-LiOONO and trans-NaOONO abs orb at (1581.6, 1580.4), (998.3, 995.6), 600.4 cm(-1) and (1549.3, 154 0.6), (996.3, 994.1), (609.4, 607.4) cm(-1), respectively; the numbers in parentheses are due to line splitting. (C) 1995 American Institute of Physics.