Bond-selective photodissociation of partially deuterated ammonia molecules: Photodissociations of vibrationally excited NHD2 in the 5νNH state and NH2D in the 5νND state

Abstract

Ultraviolet photodissociation of NHD(2) excited to the fourth overtone state of the NH stretching mode (5nu(NH)) and NH(2)D excited to that of the ND stretching mode (5nu(ND)) has been investigated by using a crossed laser and molecular beams method. Branching ratio between the NH and ND bond dissociations has been determined by utilizing a (2+1) resonance enhanced multiphoton ionization scheme of H and D atoms. For the photolysis of NHD(2) in the 5nu(NH) state, the NH dissociation cross section is 5.1+/-1.4 times as large as the ND dissociation cross section per bond. On the other hand, for the photolysis of NH(2)D in the 5nu(ND) state, the ratio of the NH dissociation cross section per bond to the ND dissociation cross section decreases to 0.68+/-0.16. In comparison with the branching ratios for the photolysis of vibrationally unexcited NH(2)D and NHD(2), the present results indicate that the excitation of the NH stretching mode enhances the NH dissociation with ca. two times larger NH/ND branching ratio, whereas the excitation of the ND stretching mode results in the preferential ND dissociation with ca. 3-4 times larger ND/NH branching ratio than that for the vibrational ground states. The mechanism of the bond-selective enhancement has been discussed in terms of the energetics and dynamics of wave packet.

Optical emission in the dissociation of ammonia by low energy He+ ions

“…More recent studies [16,17] used synchrotron radiation or other modern VUV sources. Spectroscopic control of dissociation by pumping vibrational modes with microwave photons was demonstrated in references [18][19][20].…”

The 5νNH and 5νND vibrational bands of partially deuterated ammonia species

“…Elongation of the NH bond and/or decrease in the HND bond angle are needed. According to our 3D wave packet calculation [4], the NH bond length in the 5m ND state is 1.02 Å , which is the same as NH length calculated for the ground state. Hence, the decrease in p A t is not attributable to the NH bond elongation.…”

“…After the pioneering work by CrimÕs and RosenwaksÕ groups for the HOD molecule [1,2], we recently investigated VMP of NH 3 [3], NH 2 D, and NHD 2 [4]. In comparison with HOD and NH 3 , the spectroscopic information was quite limited for NH 2 D and NHD 2 .…”

“…In particular, no data are available for the fourth ND-stretching overtone state (5m ND ) of NH 2 D and the fourth NH-stretching overtone state (5m NH ) of NHD 2 . Thus, we started a study for assigning these overtone spectra to identify the intermediate states used in our recent study of VMP [4]. Furthermore, molecular constants of these overtone states determined in the spectroscopic analysis would provide new information on the intermediate structures.…”

Communication: Mode-specific photodissociation of vibrationally excited pyrrole

“…The success in this triatomic prototype spurred additional experiments on four atom molecules, including isocyanic acid, HNCO, 21 acetylene, C 2 H 2 , and its deuterated isotopologue, C 2 HD, 22 and ammonia, NH 3 , and its single deutarated variants, NHD 2 and NH 2 D. 23,24 An even larger a) Electronic mail: ibar@bgu.ac.il.…”