Matrix samples of CH2N2/O2/Ar were photolyzed at 8thinsp;deg;K. Subsequent slow warming produced the previously observed O2thinsp;Aprime;thinsp;3Dgr;urarr;Xthinsp;3Sgr;gminus;thermoluminescence and two new progressions, one at 3100ndash;3600 Aring; and one at 3900ndash;4900 Aring;. With18O2, the 3100ndash;3600 Aring; progression displayed isotopic shifts that allow two possiblevPrime;vibrational assignments to give ngr;00= 34thinsp;730 or 33thinsp;340 (plusmn;40) cmminus;1and ohgr;ePrime;= 1390plusmn;15 cmminus;1. Similarly, the18O2shifts in the 3900ndash;4900 Aring; progression lead to two possiblevPrime; assignments to give ngr;00= 26thinsp;230 or 25thinsp;100 (plusmn;60) cmminus;1and ohgr;ePrime;= 1124plusmn;40 cmminus;1. These spectroscopic parameters point to assignments of thea3APrime;rarr;Xthinsp;1Aprime;andAprime;thinsp;1Aprime;rarr;Athinsp;1APrime;transitions of HCOOH for the 3100ndash;3600 and 3900ndash;4900 Aring; progressions, respectively. These are the first observations of such transitions of formic acid and are attributed to the CH2(3B1)+O2(3Sgr;gminus;) reaction in the cryogenic matrix.
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