Multiphoton ionization of atomic hydrogen in methane pyrolysis

The weak hydrogen bond in the fluorobenzene-ammonia van der Waals complex: Insights into the effects of electron withdrawing substituents on π versus in-plane bonding Selective OD bond dissociation of HOD: Photodissociation of vibrationally excited HOD in the 5 ν O D state Ab initio potential energy surfaces, total absorption cross sections, and product quantum state distributions for the low-lying electronic states of N 2 O J. Chem. Phys. 122, 054305 (2005); 10.1063/1.1830436Bond-selective photodissociation of partially deuterated ammonia molecules: Photodissociations of vibrationally excited NHD 2 in the 5ν NH state and NH 2 D in the 5ν ND state Ultraviolet photolysis of highly vibrationally excited NH 3 (X 1 A 1 Ј) in the 5 N-H band has been studied using a crossed laser and molecular beams method. Relative cross sections of N-H bond dissociation via the Ã ←X transition have been determined by the measurement of the action spectrum, utilizing a ͑2ϩ1͒ resonance enhanced multiphoton ionization scheme of product H atoms. The obtained cross section for the photolysis of the 4 1 ϩ 3 state ͑4 quanta in the symmetric stretching and 1 quantum in the antisymmetric stretching͒ was 1.23Ϯ0.06 times as large as that of the 5 1 state. To interpret the ratio of the obtained cross sections, we have evaluated the Franck-Condon factors for these vibrational states, by utilizing time-dependent wave-packet calculations on the potential energy surfaces constructed by an ab initio molecular orbital procedure.

Section: Methodsmentioning

confidence: 99%

Photodissociation of highly vibrationally excited NH3 in the 5νN–H region: Initial vibrational state dependence of N–H bond dissociation cross section

Akagi

Yokoyama

2003

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

Akagi

Yokoyama

2004

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.

Selective OD bond dissociation of HOD: Photodissociation of vibrationally excited HOD in the 5νOD state

Akagi¹,

Fukazawa²,

Yokoyama³

et al. 2005

Exclusively selective OD bond dissociation of HOD has been demonstrated by the ultraviolet photodissociation at 243.1 nm through the fourth overtone state of the OD stretching mode (5nu(OD)). Branching ratio between the OH and OD bond dissociation channels has been determined by detecting H and D atoms, utilizing a (2+1) resonance-enhanced multiphoton ionization (REMPI) process. The OD bond dissociation has been solely observed with the branching ratio phi(D+OH)/phi(H+OD)>12, which has been determined by the detection limit for the H atom. Time-dependent wave-packet calculations reveal two important features for the highly selective OD bond dissociation: (1) strong local-mode character of the 5nu(OD) state and (2) limitation of the total excitation energy lower than the saddle point between the OH and OD dissociation channels in the A state. Additionally, the recoil velocity and angular distribution of the nascent D atom are roughly evaluated by analyzing the Doppler-resolved REMPI spectrum. Based on these results, the dynamics of the selective OD dissociation has been discussed in detail.