Three-dimensional velocity analysis combining ion imaging with Doppler spectroscopy: Application to photodissociation of HBr at 243 nm

A formalism for calculating the angular momentum polarization of an atom or a molecule following two-photon excitation of a J-selected state is presented. This formalism is used to interpret the H atom photofragment angular distributions from single-photon dissociation of two-photon rovibronically state selected HCl and HBr prepared via a Q-branch transition. By comparison of the angular distributions measured using the velocity map imaging technique with the theoretical model it is shown that single-photon dissociation of two-photon prepared states can be used for pathway identification, allowing for the identification of the virtual state symmetry in the two-photon absorption and/or the symmetry of the dissociative state. It is also shown that under conditions of excitation with circularly polarized light, or for excitation via non-Q-branch transitions with linearly polarized light the angular momentum polarization is independent of the dynamics of the two-photon transition and analytically computable.

Section: Photodissociation Of Hbrmentioning

confidence: 99%

Section: Photodissociation Of Hbrmentioning

confidence: 99%

Two-photon state selection and angular momentum polarization probed by velocity map imaging: Application to H atom photofragment angular distributions from the photodissociation of two-photon state selected HCl and HBr

Manzhos

Romanescu

Loock

et al. 2004

“…Kinugawa and Arikawa used Doppler selection to ionize only photofragments that recoil in the plane of the detection. 24 However, this method imposes constraints on the position of the laser relative to the drift tube axis. Also Doppler selection is limited by the bandwidth of the laser and by the velocity spread of the photofragments, which can be very small for heavy fragments.…”

Section: Introductionmentioning

confidence: 99%

Photofragment imaging by sections for measuring state-resolved angle-velocity differential cross sections

Syage

1996

We describe a two-dimensional ͑2D͒ imaging technique for recording state-specific photofragment angle-velocity (,v) distributions. In these experiments the photofragment images are recorded as 2D sections of the 3D angular distributions using state-specific ionization in a time-of-flight mass spectrometer. We compare this method to previous methods that record 2D projections of the 3D distribution. The 2D sections represent cartesian flux-velocity maps in the center of mass and are related to angle-velocity differential cross sections by a simple geometric factor. Two studies are highlighted. In the first, new results are presented for the A state photodissociation of CH 3 I to CH 3 ϩI. (,v) images are presented for I atom in the 2 P 3/2 and 2 P 1/2 spin-orbit states following photodissociation at 266 and 304 nm. The principal result is detection of the weak perpendicular transitions to the 3 Q 1 state ͑at 304 nm͒ and the 1 Q state ͑at 266 nm͒ that underlie the strong parallel transition to the 3 Q 0 state. We also report the ratio of cross sections Ќ / ʈ , the anisotropy and branching ratio for I͑ 2 P 3/2 ͒ and I͑ 2 P 1/2 ͒, and the 3 Q 0 -1 Q surface crossing probability. In a second study the photodissociation of O 3 to O 2 (v)ϩO͑ 3 P jϭ2,1,0 ͒ was measured. A bimodal anisotropic velocity distribution was measured for O͑ 3 P͒ corresponding to maximum in the O 2 (v) vibrational distribution of vϭ15 and 27, in general agreement with a previous measurement. The anisotropies of the high-and low-velocity components were measured to be ␤Ϸ1.1 and 0.4, respectively.

“…[15][16][17] In the 1980s state-resolved scattering distributions of photofragments were measured by one-dimensional ͑1D͒ Doppler spectroscopy. [1][2][3][4][5][6][7][8] However, more recently, twodimensional ͑2D͒ 9-12,18 and three-dimensional ͑3D͒ ionimaging methods [19][20][21] became much more powerful experimental means for this purpose. The first observation of the -J correlation by the ion-imaging technique was reported by Houston and co-workers for O 2 (a 1 ⌬) from photodissociation of O 3 .…”

Section: Introductionmentioning

confidence: 99%

Probing the alignment of NO(X 2Π) by [2+1] resonance-enhanced multiphoton ionization via the C 2Π state: A test of semiclassical theory in 355 nm photodissociation of NO2

Katayanagi

Suzuki

1999

A theoretical method to analyze the two- and three-dimensional imaging data of photofragments with polarized angular momentum was tested by comparing with the experimental data on NO from 355 nm photodissociation of NO2. The alignment of NO(X 2Π) was detected by [2+1] resonance-enhanced multiphoton ionization via the C 2Π state. The data were analyzed by assuming the μ–ν–J triple vector correlation described by semiclassical multipole moments in the velocity-fixed frame. The geometrical factors for the two-photon absorption were derived rigorously for the intermediate coupling between Hund’s cases (a) and (b). It was also shown, however, that the geometrical factors for high J are independent of the coupling case and can be approximated by simple formulas. Excellent agreement between the simulation and the experimental data proved the validity of the semiclassical treatment.