VIBRATIONAL OVERTONE ACTIVATION OF METHYLCYCLOPROPENE

Laser vibrational overtone activation has been used to investigate the reaction channel competition in the isomerization of 1-methylcyclopro pene (MCPene). The vibrational overtone activation of three types of C H stretches (methyl, methylenic, and olefinic) in the 5 nu(CH) and 6 n u(CH) transitions initiated the isomerization and all three products ( 2-butyne, 1,3-butadiene, and 1,2-butadiene) were detected by gas chrom atography. Stern-Volmer plots were constructed for the appearance of e ach individual product and the derived experimental specific rate coef ficients were compared to those of the Rice-Ramsperger-Kassel-Marcus ( RRKM) theory. The rate coefficients for the 6 nu(CH) transitions were in good agreement with the predicted values but those for the 5 nu(CH) transition were as much as a factor of 5 too large. Product ratios of 1,3-butadiene to 2-butyne and 1,2-butadiene to 2-butyne were independ ent of pressure. In general, these ratios were lower than the RRKM pre dicted ratios due to collisional deactivation. No evidence of mode spe cific behavior was observed in these product yield ratios. (C) 1996 Am erican Institute of Physics.