Photodissociation of ammonia at 193.3 nm: Rovibrational state distribution of the NH2(Ã 2A1) fragment

The rovibrational state distribution of the nascent NH2(Ã 2A1) fragments generated by 193.3 nm photodissociation of a room temperature sample of NH3 is determined through an analysis of a major portion (6000–13 000 cm−1) of the NH2(Ã 2A1→X̃ 2B1) near infrared emission spectrum obtained by time-resolved Fourier transform infrared emission spectroscopy. The NH2(Ã) fragments are observed to be formed predominantly in their zero-point vibrational level, with substantial rotational excitation about their a-inertial axis up to the limit of the available energy, ∼3150 cm−1, but with little excitation about the other axes. The pattern of this energy disposal is discussed within the framework of existing knowledge regarding the form of the NH3 Ã state potential energy surface on which the dissociation occurs. The essential features are entirely consistent with a direct carry over, into the fragment, of the out-of-plane bending vibrational motion introduced in the parent molecule by the photoexcitation process.