Experimental and Theoretical Studies of the HeICl Van der Waals Complexes in the Valence and Ion-pair States.

The article presents results of experimental and theoretical analysis of the T-shaped and linear HeICl van der Waals complexes in the valence A1 and ion-pair ß1 states as well as the HeICl(A1,vA ,nA ←X0+ ,vX =0,nx and ß1,vß ,nß â†A1,vA ,nA ) optical transitions (ni are quantum numbers of the vdW) modes). The HeICl(ß1,vß ,nß )→He+ICl(E0+ , D ' 2 ${{D}^{{ {\prime}}}2}$ , ß1) decay are also studied. Luminescence spectra of the HeICl(ß1,vß =0-3,nß ) complex electronic (ICl(E0+ ,vE , D ' 2 , v D ' ${{D}^{{ {\prime}}}2,{v}_{{D}^{{ {\prime}}}}}$ ) and vibrational ICl(ß1,vß ) predissociation products are measured, and branching ratios of decay channels are determined. To construct potential energy surfaces for the HeICl(A1, ß1) states, we utilized the intermolecular diatomic-in-molecule perturbation theory first order method. Experimental and calculated spectroscopic characteristics of the A1 and ß1 states agree well. Comparison of the experimental and calculated pump-probe, action and excitation spectra shows that the calculated spectra describe the experimental spectra adequately.

Experimental and theoretical investigation of the ArICl van der Waals complexes in the valence and ion-pair states.

This paper presents the experimental and theoretical analyses of ArICl(IP,vIP,nIP) states' population and decay at energies lower than the ArICl(E,vE = 0,nE) dissociation limit (IP = E0+, D'2, ß1), vIP = 0, 1, and nIP are the quantum numbers of the van der Waals (vdW) modes. We have measured the excitation spectra of the ArICl(E,vE = 0,1,nE → X,vX,nX) and ArICl(ß,0,nß â†’ A and/or D',vD' ,nD' →A' luminescence as well as luminescence spectra themselves. To construct potential energy surfaces (PESs) for valence (A1, A'2) and ion-pair (E, ß, and D') electronic states of the complex, we utilized the intermolecular diatomic-in-molecule perturbation theory first order method. The experimental and calculated spectroscopic characteristics of the T-shaped ArICl valence and E, ß states agree well. The ArICl(D') state PES has no vdW levels in the T-shaped configuration, and collinear ArICl(D') binding energy is larger than that of the T-shaped ArICl(ß) state. We calculated vibrational state energies and the ArICl(IP → valence states) luminescence excitation spectra, as well as luminescence spectra themselves, by using the Heidelberg MCTDH code. The comparison of the experimental and calculated excitation spectra shows that the latter describe their principal features. The bound-bound ArICl(E,0,nE → X and ß,0,nß â†’ A) parts of experimental luminescence spectra are described adequately by the calculated spectra, whereas bound-free ArICl(E,0,nE → X, D', 0, nD' → A') parts are not described since the bound-free transitions occur in repulsive parts of the ArICl(X, A' PESs, which we cannot describe accurately.

Experimental and theoretical investigations of HeNeI2 trimer.

We report on the results of spectroscopic studies of the HeNeI2 van der Waals trimer using the two-step two-color HeNeI2(E0g +, vE = 0-3 ←hν2B0u +, vB = 19 ←hν1X0g +, vX = 0) excitation scheme. The excitation spectra of the HeNeI2(B, E) decay product luminescence and the luminescence spectra of I2 ion-pair states formed after HeNeI2(E) decay have been recorded and analyzed. The HeNeI2(X, B, E) binding energies have been estimated to be less than 111.8 cm-1, 101.6 cm-1, and 117.9 cm-1, respectively. The HeNeI2(B, vB) state decay has been found to be sequential with the formation of the HeI2(B, vB - 1) and NeI2(B, vB - 1) complexes without intermolecular excitation at the first step. An analysis of the HeNeI2(E) decay process based on the relative probabilities of the I2(D0u +) and I2(ß1g) formation after decay, as well as vibrational populations of these states obtained from luminescence spectra, has also been performed. Calculations of the HeNeI2(X, B) vibrational energies using potential energy surfaces (PESs) of HeNeI2(X, B) constructed as a sum of the HeNe, HeI2, and NeI2 potentials have been carried out. The values obtained agree well with the experimental estimations, and the observed transitions can be ascribed to the HeNeI2 trimer of a tetrahedral geometry. Besides, a comparison of the PES constructed as a sum of the coupled-cluster single double triple [CCSD(T)] potentials with the PES based on the "direct" CCSD(T) calculations has been performed for the HeNeI2(X) trimer to verify the applicability of this representation to the trimer under study.

Heterogeneous and hyperfine interactions between valence states of molecular iodine correlating with the I((2)P1/2) + I((2)P1/2) dissociation limit.

Detailed analysis of interactions between all 0g (+), 1u, and 0u (-) weakly bound states of iodine molecule correlating with the I((2)P1/2) + I((2)P1/2) (bb) dissociation limit has been performed. For this purpose, the 0u (-) (bb) state has been described using analysis of rotationally resolved excitation spectra of luminescence from the g0g (-) state populated in a three-step three-color perturbation facilitated excitation scheme via the 0u (-) state. Energies of 41 rovibrational levels, molecular constants, and potential energy curve have been determined. Energy gaps between closest rovibrational levels of the 0u (-) and 0g (+), 1u (bb) states are found to be large, ∼6 cm(-1). However, interaction of all three 0g (+), 1u, and 0u (-) (bb) states has been observed. It has been found that the 0u (-) and 1u electronic states are mixed by heterogeneous interactions, while their mixing with the 0g (+) one is due to hyperfine interactions predominantly. Admixture coefficients and electronic matrix elements of the coupling between the 0g (+) ∼1u, 0g (+)∼0u (-), and 0u (-) ∼1u states have been estimated.

Dynamics and mechanism of the E-->D, D', beta, gamma, and delta nonadiabatic transitions induced in molecular iodine by collisions with CF4 and SF6 molecules.

Nonadiabatic transitions among the first-tier ion-pair states of the iodine molecule in collisions with CF(4) and SF(6) partners are investigated by detecting the luminescence following the optical-optical double resonance excitation of the E0(g) (+)-state to the vibrational levels v(E)=8, 13, and 19. Total and partial rate constants, as well as vibrational product state distributions, are determined. It is found that electronic energy transfer in all channels is predominantly assisted by excitation of the dipole-allowed nu(3) and nu(4) modes of the partner. The measurements are accompanied by quantum scattering calculations that implement a close coupling treatment for the electronic and vibrational degrees of freedom and combine diatomics-in-molecule and long-range models for diabatic potential energy surfaces and coupling matrix elements. The analysis of experimental and theoretical data shows that the transitions without excitation of the partner are due to short-range couplings, whereas the vibrational excitation of the partner in the D0(u) (+) channel originates from the long-range coupling of two transition dipole moments: electronic of the iodine molecule and vibrational of the partner. Unexpectedly efficient excitations of the partner in the other ion-pair states, which are not coupled to the initial E0(g) (+)-state by the transition dipole, are interpreted within the postcollision mechanism. Qualitatively, this implies that during a single collision the long-range nonadiabatic transitions to D, nu(3) and D, nu(4) channels are followed by secondary short-range transitions without changing the state of the partner.