P.D. Foo

Bio: P.D. Foo is an academic researcher from Binghamton University. The author has contributed to research in topics: Molecular electronic transition. The author has an hindex of 1, co-authored 1 publications receiving 82 citations.

Fluorescence and stimulated emission S1 → S0 spectra of acetylene: Regular and ergodic regions

Abstract: The S1 → S0 transition of acetylene has been studied by spontaneous and stimulated emission. In the spontaneous emission studies, we report new data on low‐resolution dispersed fluorescence from an unrelaxed single rotational level of S1. Transitions into S0 levels from the zero‐point level up to ∼28 000 cm−1 of vibrational energy are reported. Earlier investigations of the emission from relaxed acetylene in a neon matrix and of partially relaxed fluorescence from a radio frequency discharge in acetylene have been reexamined and reinterpreted in the light of the present work. The stimulated emission study employed stimulated emission pumping (SEP) for high‐resolution investigations of two regions of S0 energies, one near 9550 cm−1 and another near 27 900 cm−1. Definite vibrational assignments were possible for most of the features observed in the lower energy region. This allowed the determination of two new vibrational constants, y224 and y244. The region near 27 900 cm−1 reveals a hitherto unobserved ki...

The electronic states of pyrrole studied by optical (VUV) absorption, near-threshold electron energy-loss (EEL) spectroscopy and ab initio multi-reference configuration interaction calculations

Abstract: A reinvestigation and extension of the observed VUV and EEL spectrum of pyrrole has been carried out, and the spectra assigned by means of high level multi-reference multi-root CI studies. A similar reasssessment of the UV-photoelectron spectrum leads to the conclusion that our previous assignment of IP3 to ionisation of the inner π-level (1b1) is correct and that most other assignments to ionisation of a σ-electron are incorrect. This is supported by the calculation of a wide range of Rydberg states derived from the five least bound orbitals, in the IP order: 1a2−1 1 ππ ∗ states of symmetry 1A1 and 1B2. The range of calculated valence states of ππ ∗ -type has been extended to include those from 1b1.

Triplet electronic states of acetylene: cis and trans structures and energetics

Abstract: Molecular electronic structure theory has been used to predict the equilibrium geometries and energies of acetylene in its ground state and lowest triplet electronic states. Both double zeta (DZ) and double zeta plus polarization (DZ+P) basis sets of Gaussian functions were used, in conjunction with self‐consistent‐field (SCF) and large scale configuration interaction (CI) wavefunctions. The predicted 1Σ+g ground state structure is re(C–C) =1.213 A, re(C–H) =1.066 A, in good agreement with experiment, re(C–C) =1.203 A, re(C–H) =1.060 A. The first excited state of acetylene is the cis 3B2 state, predicted to lie 3.43 eV above the 1Σ+g ground state. The predicted equilibrium geometry of this cis state is re(C–C) =1.343 A, ϑe(HCC) =127.8°, re(C–H) =1.090 A. The three other lowest triplet states are trans 3Bu (Te=3.78 eV), trans 3Au (4.13) eV, and cis 3A2 (4.50 eV). The predicted ordering and CCH bond angles for these states are not entirely consistent with Walsh’s rules.

Photochemistry of acetylene at 1849 Å

Abstract: It is pointed out that the photochemistry of acetylene in the 1500-2000 A region at low pressure, particularly the quantum yield of C2H production and the reactions of C2H with H2 and hydrocarbons, is important in understanding the photochemistry of Jovian and Titan atmospheres. The present investigation was initiated to obtain information on these issues. The 1849 A light source used in the study was a sealed quartz tube containing a drop of Hg and 2 torr of Ar excited by a microwave generator. The lamp was attached to a Pyrex reaction cell. The amount of diacetylene produced was measured on the basis of absorption near 1650 A. Reaction mixtures of acetylene with N2, He, C2H6, or C3H8 were prepared. Attention is given to the absorption cross section, the photolysis of acetylene, and the photolysis of acetylene in the presence of other gases. It is found that the photochemical process of acetylene at 1849 A may represent that of acetylene in the Titan atmosphere.