Time-Resolved Spectroscopy

An Experimental Perspective

Thomas Weinacht, Brett J. Pearson

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9780367780401
• eBook ISBN: 9780429804175
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physics
• Index: Physics

This concise and carefully developed text offers a reader friendly guide to the basics of time-resolved spectroscopy with an emphasis on experimental implementation. The authors carefully explain and relate for the reader how measurements are connected to the core physical principles. They use the time-dependent wave packet as a building block for understanding quantum dynamics, progressively advancing to more complex topics. The topics are discussed in paired sections, one discussing the theory and the next presenting the related experimental methods.

A wide range of readers including students and newcomers to the field will gain a clear and practical understanding of how to measure aspects of molecular dynamics such as wave packet motion, intramolecular vibrational relaxation, and electron-electron coupling, and how to describe such measurements mathematically.

PART I

Introduction and Background

CHAPTER 1

Introduction

1.1 WHAT IS TIME-RESOLVED SPECTROSCOPY?

Our experience of life is time dependent—things move, changing their position or velocity with time. Yet quantum mechanics, which governs life at the atomic and molecular level and is one of the most successful theories of modern physics, is generally formulated in terms of time-independent quantities. Most early tests of quantum mechanics aimed to measure these time-independent quantities such as the energy levels of atoms or molecules. This approach is quite sensible when looking for analytic solutions to the differential equations that govern quantum mechanics, particularly for simple, isolated systems. The differential equations are often separable into temporal and spatial components, allowing one to find time-independent solutions relatively easily. The full time-dependent solutions are then built from linear combinations of the stationary results.

However, if we are interested in following dynamics and understanding how systems evolve, a time-dependent perspective is more useful. Time-resolved measurements have the potential to provide the most direct information about dynamics, particularly for many-body systems and those not isolated from their environment. The focus of this book is therefore to study physical systems from a time-dependent perspective: how do systems evolve in time, and how can we measure this evolution?

We are specifically interested in studying fundamental systems at the atomic and molecular level, where the laws of quantum mechanics dictate the dynamics. In quantum mechanics, the complex wave function Ψ(r, t) provides a complete description of the system; at any given time, knowledge of Ψ(r, t) yields information about an object’s dynamical variables such as position, momentum, or energy. These quantities are called observables, as one can measure (observe) their values in a given system. Time-resolved spectroscopy involves measuring observables for quantum systems whose wave functions are prepared in a well-defined initial state and subsequently evolve in time.

While the dream of time-resolved measurements is to make real-time “molecular movies” of dynamics, it is rare that one can directly measure evolution of the molecular structure or wave function. Rather, insight is typically gained by comparing experimental measurements with theoretical calculations of observables. The experimentally tested calculations can then be used to generate the molecular movie. Thus, an important criterion when evaluating different measurement approaches is how easily they can be compared with calculations of the observable. Throughout the book, we highlight how experimental techniques are closely coupled to the theory a...

Table of contents

• Cover
• Half Title
• Series Page
• Title Page
• Copyright Page
• Dedication Page
• Table of Contents
• Preface
• Authors
• Part I Introduction and Background
• Part II Quantum Dynamics in One Dimension
• Part III Measurements of One Dimensional Dynamics
• Part IV Quantum Dynamics in Multiple Dimensions
• Part V Measurements of Multidimensional Dynamics
• Appendix A Quantum Mechanics Essentials
• Appendix B Experimental Considerations
• Appendix C Additional Problems
• Bibliography
• Index