Abstract:

The absorption spectrum of the N2O molecule in the wavelength range of 143.6-146.9 nm was measured under the jet-cooled condition by using the high resolution vacuum ultraviolet radiation, which was generated by resonance-enhanced difference-frequency mixing, corresponding to the C1∏←X1∑+ transition. Three vibrational bands were observed with frequency intervals of 521 and 482 cm -1, and they were superimposed on a wide absorption background. Previous high-level quantum chemical calculations indicate that the C1∏ state of N2O is dissociative along the N—O elongation, while it is bound along the N—N bond stretching or N2O bending. Therefore, the observed vibrational progression is a Feshbach resonance of the dissociative transition state. From an anti-Fourier transformation analysis, the recurrence period of the unstable periodic orbit of the Feshbach resonance was found to be 61 fs and the corresponding vibrational frequency was 546 cm-1. Since this vibrational frequency is close to the frequency of the bending motion, the unstable periodic orbit is mostly composed of the bending motion of the C1∏ state coupled with dissociation. The N—N stretching vibration does not participate in its formation. Therefore, we describe the excitation-dissociation dynamics of the C1∏state of N2O clearly.

Key words: Absorption spectrum, N2O, Vacuumultraviolet, Dissociation