Torsional energy levels of CH3OH+/CH3OD+/CD3OD+ studied by zero-kinetic energy photoelectron spectroscopy and theoretical calculations

Abstract

The torsional energy levels of CH3OH(+), CH3OD(+), and CD3OD(+) have been determined for the first time using one-photon zero kinetic energy photoelectron spectroscopy. The adiabatic ionization energies for CH3OH, CH3OD, and CD3OD are determined as 10.8396, 10.8455, and 10.8732 eV with uncertainties of 0.0005 eV, respectively. Theoretical calculations have also been performed to obtain the torsional energy levels for the three isotopologues using a one-dimensional model with approximate zero-point energy corrections of the torsional potential energy curves. The calculated values are in good agreement with the experimental data. The barrier height of the torsional potential energy without zero-point energy correction was calculated as 157 cm(-1), which is about half of that of the neutral (340 cm(-1)). The calculations showed that the cation has eclipsed conformation at the energy minimum and staggered one at the saddle point, which is the opposite of what is observed in the neutral molecule. The fundamental C-O stretch vibrational energy level for CD3OD(+) has also been determined. The energy levels for the combinational excitation of the torsional vibration and the fundamental C-O stretch vibration indicate a strong torsion-vibration coupling.

Absolute Photoabsorption Cross-Sections of Methanol for Terrestrial and Astrophysical Relevance

“…These are also in good agreement with the present value of 342 cm –1 (Figure S7). The zero-kinetic energy photoelectron spectroscopy and theoretical calculations of Dai et al report a 157 cm –1 barrier height for the ion, in good agreement with the corresponding result of 150 cm –1 from Macneil and Dixon . For the 3s and 3p Rydberg states, our barrier values vary from 141 to 393 cm –1 (Figures S8–S11), with such differences attributed to the spatial extension of the occupied Rydberg orbital, which renders rotation to the methyl group.…”

“…with the V 0 , V 3 , V 6 , V 9 , and V 12 values and corresponding torsional potential energy scans, being given in Figures S7−S11 (Supporting Information) for the ground, 3sσ, 3pσ and 3pπ states. Dai et al 60 report a ground-state barrier (without ZPE correction) of about 340 cm −1 , Bowman et al 59 obtained a value of 342.1 cm −1 , while Macneil and Dixon 32 report an internal barrier to rotation of <400 cm −1 . The experimental data of Xu and Hougen 61 yields 373.59 cm −1 .…”

“…Dai et al report a ground-state barrier (without ZPE correction) of about 340 cm –1 , Bowman et al obtained a value of 342.1 cm –1 , while Macneil and Dixon report an internal barrier to rotation of <400 cm –1 . The experimental data of Xu and Hougen yields 373.59 cm –1 .…”

Mechanistical study on the formation of hydroxyacetone (CH3COCH2OH), methyl acetate (CH3COOCH3), and 3-hydroxypropanal (HCOCH2CH2OH) along with their enol tautomers (prop-1-ene-1,2-diol (CH3C(OH)CHOH), prop-2-ene-1,2-diol (CH2C(OH)CH2OH), 1-methoxyethen-1-ol (CH3OC(OH)CH2) and prop-1-ene-1,3-diol (HOCH2CHCHOH)) in interstellar ice analogs

“…Note that the computed IEs are also valid for (partially) deuterated products considering only slight changes in their ionization energies by less than 0.01 eV for the partially deuterated products. 36,69 The decrease of 0.03 eV for the IEs caused by the electric field of ion optics was considered during the IE error analysis (Table S1, ESI †). 70…”

Quantum Tunneling Mediated Low-Temperature Synthesis of Interstellar Hemiacetals

“…For CH 3 CHO–CH 3 OH ice, data recorded at 10.49 eV reveal a prominent signal at a mass-to-charge ratio ( m / z ) of 61 along with the acetaldehyde (IE = 10.229 ± 0.0007 eV) at m / z = 44. Note that methanol (IE = 10.8393 ± 0.0005 eV) cannot be detected since its ionization energy is higher than 10.49 eV. It is important to stress that no signal for 1-methoxyethanol parent radical cation ( 1 •+ , CH 3 OCH­(OH)­CH 3 · + ) at m / z = 76 was detected due to dissociative photoionization.…”