Towards the complete experiment: measurement of S(1D2) polarization in correlation with single rotational states of CO(J) from the photodissociation of oriented OCS(v2 = 1|JlM = 111)

Abstract

In this paper we report slice imaging polarization experiments on the state-to-state photodissociation at 42,594 cm(-1) of spatially oriented OCS(v(2) = 1|JlM = 111) → CO(J) + S((1)D(2)). Slice images were measured of the three-dimensional recoil distribution of the S((1)D(2)) photofragment for different polarization geometries of the photolysis and probe laser. The high resolution slice images show well separated velocity rings in the S((1)D(2)) velocity distribution. The velocity rings of the S((1)D(2)) photofragment correlate with individual rotational states of the CO(J) cofragment in the J(CO) = 57-65 region. The angular distribution of the S((1)D(2)) velocity rings are extracted and analyzed using two different polarization models. The first model assumes the nonaxial dynamics evolves after excitation to a single potential energy surface of an oriented OCS(v(2) = 1|JlM = 111) molecule. The second model assumes the excitation is to two potential energy surfaces, and the OCS molecule is randomly oriented. In the high J region (J(CO) = 62-65) it appears that both models fit the polarization very well, in the region J(CO) = 57-61 both models seem to fit the data less well. From the molecular frame alignment moments the m-state distribution of S((1)D(2)) is calculated as a function of the CO(J) channel. A comparison is made with the theoretical m-state distribution calculated from the long-range electrostatic dipole-dipole plus quadrupole interaction model. The S((1)D(2)) photofragment velocity distribution shows a very pronounced strong peak for S((1)D(2)) fragments born in coincidence with CO(J = 61).

The ultraviolet spectrum of OCS from first principles: Electronic transitions, vibrational structure and temperature dependence

“…Comparisons between computed and observed 22,23,26,31,34,37,39 angular distribution parameters β suggest that either our A state TDM function is directed too closely along the OCS axis, or we have underestimated the contributions of the B and C states to the electronic absorption for the lower j part of the rotational distribution. The measured alignment parameters A (2) 0 also suggest that the contributions of B and C may be more important than our computed TDM functions indicate.…”

“…20 The details of photofragmentation in the first absorption band have been the focus of many experimental studies. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] The absorption cross section increases significantly with excitation of the bending mode in the ground state. 28,32,36 The fragmentation yields sulfur atoms in both the singlet and triplet states with a branching ratio of about 0.95:0.05 at the absorption peak.…”

“…The product angular distribution has been studied extensively in several laboratories and a strong variation of the β parameter with the CO rotational state has been observed. 23,26,31,34,37,39 In contrast to the many experimental investigations there have been only a few theoretical studies of the photodissociation process. In a joint experimental and theoretical paper Suzuki et al 26 calculated potential energy surfaces (PES) and transition dipole moment (TDM) functions for the lowest singlet electronic states.…”

Ultraviolet photodissociation of OCS: Product energy and angular distributions

“…Brouard et al 3 and Lipciuc et al 4 have provided good recent reviews. The absorption spectrum has a broad Gaussian-like profile with pronounced vibrational structures.…”

“…The angular distribution of the products, characterized by the parameter β, has been measured for several wavelengths as function of j. 3,4,[7][8][9][10][11][12] β shows a strong variation with j for all wavelengths. It has small positive values in the range of the main peak of the rotational distribution but increases steeply to almost the maximum possible value of 2 in the range of the second maximum of P j .…”