Photo-Absorption Studies on Formaldehyde Using Synchrotron Radiation at Indus I

Abstract

Photo-absorption spectra of formaldehyde (HCHO) is recorded in the range of 6-11.5 eV at various pressures (<0.001-2 mbar) at an average resolution of 1.2 Å using Photophysics beam line at the 450 MeV Indus-1 synchrotron radiation facilities at RRCAT Indore, India. The spectrum is found to consist exclusively of n ! Rydberg transitions converging to the ground state of HCHO þ . The highest identified Rydberg states, observed up to the first ionization limit of HCHO, correspond to 7s, 11p, 9d, and 12f orbitals. Analyzed electronic spectrum along with the intensities and quantum defects are presented. To interpret the observed weak valence transitions instead of strong valence transitions, a theoretical study of Rydberg and valence electronic states of HCHO is performed in the framework of single configuration interaction (CIS) and time-dependent density functional theory (TDDFT) using different basis sets. Electronic transition energies of high-lying singlet and triplet valence states as calculated using TDDFT (B3LYP) level of theory are found to give fairly-good agreement with the experimental data.

Towards the assignment of the REMPI spectrum of Ph2O using CIS and TD-DFT methods

“…Considering the ionisation energy, we emphasise the remarkable agreement between the B3LYP calculated value and the experimental value by Paiva et al [7], which differ by 0.5 %, and the FCI calculated value lies more than 0.5 eV above the result of Terlouw et al The 5.5 eV energy value for the S 0 →S 1 transition, calculated in the CIS framework, is in good agreement, given the well documented overestimation of CIS excitation energies [32][33][34], with the experimental values of 4.55 ± 0.01 eV and 4.45 ± 0.01 eV, obtained by Uno et al [5] and Paiva et al [10], respectively.…”

“…The experimental excitation energy of Uno et al [5] and experimental ionisation energies of Terlouw et al [6] and Paiva et al [7] are also shown for comparison. It is well documented in the literature [32][33][34] that the CIS method overestimates excitation energies substantially (typically by 1-2 eV), hence we can compare the excitation energy of 5.5 eV, obtained in Table 3. Experimental and theoretical adiabatic ionisation energies ( E) and first excited-state transition energy of diphenyl ether (Ph 2 O).…”

Identifying Thermal Decomposition Products of Nitrate Ester Explosives Using Gas Chromatography–Vacuum Ultraviolet Spectroscopy: An Experimental and Computational Study

“…8) is composed of vibronic Rydberg transitions where the Rydberg transitions are intense and the vibrational progression are weak. 81,82 The Rydberg transitions resulting from the ground state ( 1 A 1 ) have been previously observed using a VGA 101 VUV spectrometer. 81,[83][84][85] However, the vibrational transitions were not distinguishable.…”