Tunable far-infrared spectroscopy of malonaldehyde

124

Since the earliest explorations of quantum mechanics, it has been a topic of great interest that quantum tunneling allows particles to penetrate classically insurmountable barriers. Instanton theory provides a simple description of these processes in terms of dominant tunneling pathways. Using a ring-polymer discretization, an efficient computational method is obtained for applying this theory to compute reaction rates and tunneling splittings in molecular systems. Unlike other quantum-dynamics approaches, the method scales well with the number of degrees of freedom, and for many polyatomic systems, the method may provide the most accurate predictions which can be practically computed. Instanton theory thus has the capability to produce useful data for many fields of low-temperature chemistry including spectroscopy, atmospheric and astrochemistry, as well as surface science. There is however still room for improvement in the efficiency of the numerical algorithms, and new theories are under development for describing tunneling in nonadiabatic transitions.

Section: Tunneling Splittingsmentioning

confidence: 99%

Perspective: Ring-polymer instanton theory

Richardson

2018

124

“…The column labeled Rule indicates which of Rules I-V governs the relative increase or decrease of the splitting compared to the observed zero-point splitting of 21.58 cm −1 . 15 The normal-mode couplings leading to local modes, listed in the last column, are derived from the Dushinsky matrix elements according to Eq. (1); observing splittings in the higher energy region is both more difficult and less informative than in the lower energy region.…”

Section: Rule V: Excitation Of Any Mode That Interchanges With Any Otmentioning

confidence: 99%

Communication: Selection rules for tunneling splitting of vibrationally excited levels

Siebrand

Smedarchina²,

Fernández‐Ramos

2013

“…Early experimental investigations on the tunneling splitting [1][2][3][4] on MA sparked a series of theoretical studies aiming to understand the nature of its ground vibrational state. The early theoretical works of Carrington and Miller 5,6 have shown that a one-dimensional effective treatment of the proton tunneling on MA is fundamentally flawed.…”

Section: Introductionmentioning

confidence: 99%

The ground state tunneling splitting of malonaldehyde: Accurate full dimensional quantum dynamics calculations

Coutinho-Neto

Viel

Manthe

2004

123

102

Benchmark calculations of the tunneling splitting in malonaldehyde using the full dimensional potential proposed by Yagi et al. [J. Chem. Phys. 115, 10647 (2001)] are reported. Two exact quantum dynamics methods are used: the multiconfigurational time-dependent Hartree (MCTDH) approach and the diffusion Monte Carlo based projection operator imaginary time spectral evolution (POITSE) method. A ground state tunneling splitting of 25.7±0.3 cm−1 is calculated using POITSE. The MCTDH computation yields 25 cm−1 converged to about 10% accuracy. These rigorous results are used to evaluate the accuracy of approximate dynamical approaches, e.g., the instanton theory.