Effective potential energy surface of HD16O for calculation of highly excited states of nν3 and ν1 + nν3 types

Abstract

133Potential energy surfaces (PES) and dipole moment surfaces (DMS) of a molecule determine its physical and chemical properties; therefore, their retrieval from spectra is one of the most important problems of rotational vibrational (RV) spectroscopy. In recent years, significant progress in the accuracy of variational calculations of energy levels of triatomic molecules was observed, as applied to water as one of the most studied molecules, on the basis of improved PES [1,2].Despite the fact that PES for different water vapor isotopologues has been studied for a long time in many works, errors of 100 cm -1 were not uncommon and were typical, and an accuracy of 1 cm -1 for calculated energy levels was acceptable. Partridge and Schwenke [1, 2] firstly achieved an accuracy of ∼0.1 cm -1 for band centers and about 10% for intensities of calcu lated water vapor spectra, based on an ab initio PES, optimized through fitting to experimental energy lev els and an ab initio DMS. Band centers and intensities of RV transitions in [1,2] were computed with the use of a variational method.Transitions to nν 3 and ν 1 + nν 3 states are the stron gest in the spectrum; therefore, they are the most stud ied and promising for further investigations in the UV spectral range.The first detailed analysis of the accuracy of calcu lation [1] for H 2 16 O energy levels was made in [3]. Cal culation results were compared with a large amount of experimental data, including experimental levels, which were not used in the PES calculation in [1]. The analysis confirmed high accuracy and good extrapola tion properties of the calculation [1]. Later, the Par tridge and Schwenke potential [1, 2] was improved in [4], where PES was used for calculation of the H 2 16 O line list known as BT2 (by names of authors Barber and Tennyson) [5], which is currently the fullest and includes more than 500000000 transitions in a range up to 30000 cm -1 . Currently, work on the improve ment and optimization of PES continues for the basic water vapor isotopologues (see, e.g., [6-9]).The potential energy surface of the HD 16 O isoto pologue has been studied much less. Following the calculation of RV energy levels by Schwenke and Par tridge [1, 2], centers and intensities of RV transitions of HD 16 O were computed with a high accuracy by S. A. Tashkun. These results are accessible on the web site (http://spectra.iao.ru) (see [10]). The calculations were made on the basis of PES and DMS [1, 2], but with the use of a larger basis set. Finally, in [11], a PES was described (further called HDO_07) which allowed the representation of experimental RV energy levels, included in the fitting, up to 25000 cm -1 with a rms error of 0.035 cm -1 (in calculations [1, 2], the rms error was 0.45 cm -1 ). Based on the HDO_07 PES and dipole moment [12], a HDO RV line list has been calculated known as VTT (Voronin, Tennison, Tolchenov) [13], which is currently the fullest and the most accurate. VTT includes 697454528 transitions of HD 16 O in a range up to 25600 cm -1 . The further r...

Empirical normal intensity distribution for overtone vibrational spectra of triatomic molecules

“…Therefore, if such high precision is required for calculated transition intensities, one needs to extend the repulsive wall of the ab initio potential up to very high energies, as we have done for CO [29]. Note that using ab initio data to avoid unphysical behavior of the potential at short inter-atomic separations has already become common practice [30,31].…”