A refined quartic potential energy surface and large scale vibrational calculations for S0 thiophosgene.

In this work we present a full 6D quartic potential energy surface (PES) for S0 thiophosgene in curvilinear symmetrized bond-angle coordinates. The PES was refined starting from an ab initio field derived from acc-pVTZ basis set with CCSD(T) corrections for electron correlation. In the present calculations we used our variational method that was recently tested on formaldehyde and some of its isotopomers, along with additional improvements.

Variational study on the vibrational level structure and vibrational level mixing of highly vibrationally excited S₀ D₂CO.

We perform converged high precision variational calculations to determine the frequencies of a large number of vibrational levels in S(0) D(2)CO, extending from low to very high excess vibrational energies. For the calculations we use our specific vibrational method (recently employed for studies on H(2)CO), consisting of a combination of a search/selection algorithm and a Lanczos iteration procedure. Using the same method we perform large scale converged calculations on the vibrational level spectral structure and fragmentation at selected highly excited overtone states, up to excess vibrational energies of ∼17,000 cm(-1), in order to study the characteristics of intramolecular vibrational redistribution (IVR), vibrational level density and mode selectivity.

Variational study on the vibrational level structure and IVR behavior of highly vibrationally excited S0 formaldehyde.

We perform large scale converged variational vibrational calculations on S(0) formaldehyde up to very high excess vibrational energies (E(v)), E(v)∼17,000cm(-1), using our vibrational method, consisting of a specific search/selection/Lanczos iteration procedure. Using the same method we investigate the vibrational level structure and intramolecular vibrational redistribution (IVR) characteristics for various vibrational levels in this energy range in order to assess the onset of IVR.

Rotational level involvement in the T1-->S0 intersystem crossing transition in thiophosgene.

We propose and develop theoretically a general mechanism for the involvement of rotational motion into the nonradiative transitions that occur in an isolated polyatomic molecule. The treatment is based on the different rotational constants and different (asymmetric top-symmetric top) molecular structures in the two combining electronic states. We focus our attention on the T(1)-->S(0) intersystem crossing (ISC) transition in thiophosgene and show how the rotational mechanism could lead to a considerable enhancement in the effective level density for the process.

A combined theoretical treatment of T(1)-->S(0) intersystem crossing and intramolecular vibrational redistribution in thiophosgene.

We combine our two recent theoretical approaches for electronic relaxation T(1)-->S(0) and vibrational relaxation processes in thiophosgene (SCCl(2)) to provide a more detailed picture of the intersystem crossing (ISC) and phosphorescence from the first triplet T(1). Our analysis shows that ISC is not a true irreversible decay and should lead to violent phosphorescence quantum beats that could be observed experimentally.

Symmetry segregation of the vibronic levels within the S1<--S0 system of thiophosgene, Cl2CS, by optical-optical double resonance spectroscopy.

The first singlet-singlet electronic system, S1<--S0, in thiophosgene has been recorded as a laser induced fluorescence (LIF) excitation and an optical-optical double resonance (OODR) spectrum under jet-cooled conditions. In the OODR process, the sum of the frequencies of the pump and probe lasers must be fixed to the energy difference between a pair of vibronic levels in the S2(v') and S0(v") states. Detection is through the fluorescence from the S2 state.

Empirical determination of the harmonic force constants in benzene. 4. The Fermi resonances.

In this article, we present a continuation of our work on the refinement of the harmonic force constants Fi,k in benzene (in symmetrized Whiffen's coordinates) and on a growing number of higher order (anharmonic) force constants, Fi,j,k and Fi,j,k,l, that are of importance for the benzene isotopomer invariant potential energy surface. The refined set of harmonic and anharmonic force constants improves the agreement between the experimental levels and those calculated theoretically. The emphasis of the present work is on the analysis of the two notable Fermi resonances in benzene (nu8 +nnu1 <=> (n +1)nu1 + nu6, where n = 0, 1, .

An optical-optical double resonance probe of the lowest triplet state of jet-cooled thiophosgene: rovibronic structures and electronic relaxation.

The vibrational structure, rotational structure, and electronic relaxation of the "dark" T1 3A2(n,pi*) state of jet-cooled thiophosgene have been investigated by two-color S2<--T1<--S0 optical-optical double resonance (OODR) spectroscopy, which monitors the S2-->S0 fluorescence generated by S2<--T1 excitation. This method is capable of isolating the T1 vibrational structure into a1, b1, and b2 symmetry blocks. The fluorescence-detected vibrational structure of the Tz spin state of T1 shows that the CS stretching frequency as well as the barrier height for pyramidal deformation are significantly greater in the 3A2(n,pi*) state than in the corresponding 1A2(n,pi*) state.

Analysis of the High-Resolution Rotational Structure of the Origin and First Torsional Members of the 267-nm Band System of Formic Acid.

The fluorescence excitation spectrum of formic acid monomer (HCOOH) was recorded in the 268-257 nm region under relatively high resolution. The cooling conditions of a rotating slit-jet nozzle simplified the rotational structure and allowed for a combination line-by-line least-squares/band-contour analysis and the determination of the rotational constants. The 0(0)(0) and 9(1)(0) bands were each simultaneously fitted to a combination of c-type and b-type bands.