If we assume the vibrational efficacy to be 1, we would expect S 0 to increase by a factor of two, which would be clearly discernible in our measurements. However, our results clearly show that there is no such increase. Based on the uncertainty in S 0 estimation, we conclude that the upper limit of vibrational efficacy for this system is 0.25. This is rather surprising since several studies have indicated that the transition state has a bent configuration in dissociative chemisorption of CO 2 on various metal surfaces. Interestingly, for the closely related system of CO 2 dissociation on Ni(100), a factor of 2-10 increase in S 0 was observed at a 1000 K nozzle temperature compared to 300 K. Similarly, a recent study of CO 2 on an H-covered Cu(111) and Cu(100) surface reported a vibrational efficacy of 8-9 for the hydrogen pickup reaction through the Eley-Rideal mechanism. A recent study of CO 2 dissociation dynamics on Cu(110) using multidimensional PES also suggests that excitation of bending vibrational mode enhances the reaction probabilities. These findings are in contrast with our observation where no vibration enhancement is seen.